[SPARK-1103] Automatic garbage collection of RDD, shuffle and broadcast data

This PR allows Spark to automatically cleanup metadata and data related to persisted RDDs, shuffles and broadcast variables when the corresponding RDDs, shuffles and broadcast variables fall out of scope from the driver program. This is still a work in progress as broadcast cleanup has not been implemented.

**Implementation Details**
A new class `ContextCleaner` is responsible cleaning all the state. It is instantiated as part of a `SparkContext`. RDD and ShuffleDependency classes have overridden `finalize()` function that gets called whenever their instances go out of scope. The `finalize()` function enqueues the object’s identifier (i.e. RDD ID, shuffle ID, etc.) with the `ContextCleaner`, which is a very short and cheap operation and should not significantly affect the garbage collection mechanism. The `ContextCleaner`, on a different thread, performs the cleanup, whose details are given below.

*RDD cleanup:*
`ContextCleaner` calls `RDD.unpersist()` is used to cleanup persisted RDDs. Regarding metadata, the DAGScheduler automatically cleans up all metadata related to a RDD after all jobs have completed. Only the `SparkContext.persistentRDDs` keeps strong references to persisted RDDs. The `TimeStampedHashMap` used for that has been replaced by `TimeStampedWeakValueHashMap` that keeps only weak references to the RDDs, allowing them to be garbage collected.

*Shuffle cleanup:*
New BlockManager message `RemoveShuffle(<shuffle ID>)` asks the `BlockManagerMaster` and currently active `BlockManager`s to delete all the disk blocks related to the shuffle ID. `ContextCleaner` cleans up shuffle data using this message and also cleans up the metadata in the `MapOutputTracker` of the driver. The `MapOutputTracker` at the workers, that caches the shuffle metadata, maintains a `BoundedHashMap` to limit the shuffle information it caches. Refetching the shuffle information from the driver is not too costly.

*Broadcast cleanup:*
To be done. [This PR](https://github.com/apache/incubator-spark/pull/543/) adds mechanism for explicit cleanup of broadcast variables. `Broadcast.finalize()` will enqueue its own ID with ContextCleaner and the PRs mechanism will be used to unpersist the Broadcast data.

*Other cleanup:*
`ShuffleMapTask` and `ResultTask` caches tasks and used TTL based cleanup (using `TimeStampedHashMap`), so nothing got cleaned up if TTL was not set. Instead, they now use `BoundedHashMap` to keep a limited number of map output information. Cost of repopulating the cache if necessary is very small.

**Current state of implementation**
Implemented RDD and shuffle cleanup. Things left to be done are.
- Cleaning up for broadcast variable still to be done.
- Automatic cleaning up keys with empty weak refs as values in `TimeStampedWeakValueHashMap`

Author: Tathagata Das <tathagata.das1565@gmail.com>
Author: Andrew Or <andrewor14@gmail.com>
Author: Roman Pastukhov <ignatich@mail.ru>

Closes #126 from tdas/state-cleanup and squashes the following commits:

61b8d6e [Tathagata Das] Fixed issue with Tachyon + new BlockManager methods.
f489fdc [Tathagata Das] Merge remote-tracking branch 'apache/master' into state-cleanup
d25a86e [Tathagata Das] Fixed stupid typo.
cff023c [Tathagata Das] Fixed issues based on Andrew's comments.
4d05314 [Tathagata Das] Scala style fix.
2b95b5e [Tathagata Das] Added more documentation on Broadcast implementations, specially which blocks are told about to the driver. Also, fixed Broadcast API to hide destroy functionality.
41c9ece [Tathagata Das] Added more unit tests for BlockManager, DiskBlockManager, and ContextCleaner.
6222697 [Tathagata Das] Fixed bug and adding unit test for removeBroadcast in BlockManagerSuite.
104a89a [Tathagata Das] Fixed failing BroadcastSuite unit tests by introducing blocking for removeShuffle and removeBroadcast in BlockManager*
a430f06 [Tathagata Das] Fixed compilation errors.
b27f8e8 [Tathagata Das] Merge pull request #3 from andrewor14/cleanup
cd72d19 [Andrew Or] Make automatic cleanup configurable (not documented)
ada45f0 [Andrew Or] Merge branch 'state-cleanup' of github.com:tdas/spark into cleanup
a2cc8bc [Tathagata Das] Merge remote-tracking branch 'apache/master' into state-cleanup
c5b1d98 [Andrew Or] Address Patrick's comments
a6460d4 [Andrew Or] Merge github.com:apache/spark into cleanup
762a4d8 [Tathagata Das] Merge pull request #1 from andrewor14/cleanup
f0aabb1 [Andrew Or] Correct semantics for TimeStampedWeakValueHashMap + add tests
5016375 [Andrew Or] Address TD's comments
7ed72fb [Andrew Or] Fix style test fail + remove verbose test message regarding broadcast
634a097 [Andrew Or] Merge branch 'state-cleanup' of github.com:tdas/spark into cleanup
7edbc98 [Tathagata Das] Merge remote-tracking branch 'apache-github/master' into state-cleanup
8557c12 [Andrew Or] Merge github.com:apache/spark into cleanup
e442246 [Andrew Or] Merge github.com:apache/spark into cleanup
88904a3 [Andrew Or] Make TimeStampedWeakValueHashMap a wrapper of TimeStampedHashMap
fbfeec8 [Andrew Or] Add functionality to query executors for their local BlockStatuses
34f436f [Andrew Or] Generalize BroadcastBlockId to remove BroadcastHelperBlockId
0d17060 [Andrew Or] Import, comments, and style fixes (minor)
c92e4d9 [Andrew Or] Merge github.com:apache/spark into cleanup
f201a8d [Andrew Or] Test broadcast cleanup in ContextCleanerSuite + remove BoundedHashMap
e95479c [Andrew Or] Add tests for unpersisting broadcast
544ac86 [Andrew Or] Clean up broadcast blocks through BlockManager*
d0edef3 [Andrew Or] Add framework for broadcast cleanup
ba52e00 [Andrew Or] Refactor broadcast classes
c7ccef1 [Andrew Or] Merge branch 'bc-unpersist-merge' of github.com:ignatich/incubator-spark into cleanup
6c9dcf6 [Tathagata Das] Added missing Apache license
d2f8b97 [Tathagata Das] Removed duplicate unpersistRDD.
a007307 [Tathagata Das] Merge remote-tracking branch 'apache/master' into state-cleanup
620eca3 [Tathagata Das] Changes based on PR comments.
f2881fd [Tathagata Das] Changed ContextCleaner to use ReferenceQueue instead of finalizer
e1fba5f [Tathagata Das] Style fix
892b952 [Tathagata Das] Removed use of BoundedHashMap, and made BlockManagerSlaveActor cleanup shuffle metadata in MapOutputTrackerWorker.
a7260d3 [Tathagata Das] Added try-catch in context cleaner and null value cleaning in TimeStampedWeakValueHashMap.
e61daa0 [Tathagata Das] Modifications based on the comments on PR 126.
ae9da88 [Tathagata Das] Removed unncessary TimeStampedHashMap from DAGScheduler, added try-catches in finalize() methods, and replaced ArrayBlockingQueue to LinkedBlockingQueue to avoid blocking in Java's finalizing thread.
cb0a5a6 [Tathagata Das] Fixed docs and styles.
a24fefc [Tathagata Das] Merge remote-tracking branch 'apache/master' into state-cleanup
8512612 [Tathagata Das] Changed TimeStampedHashMap to use WrappedJavaHashMap.
e427a9e [Tathagata Das] Added ContextCleaner to automatically clean RDDs and shuffles when they fall out of scope. Also replaced TimeStampedHashMap to BoundedHashMaps and TimeStampedWeakValueHashMap for the necessary hashmap behavior.
80dd977 [Roman Pastukhov] Fix for Broadcast unpersist patch.
1e752f1 [Roman Pastukhov] Added unpersist method to Broadcast.
[SPARK-1331] Added graceful shutdown to Spark Streaming

Current version of StreamingContext.stop() directly kills all the data receivers (NetworkReceiver) without waiting for the data already received to be persisted and processed. This PR provides the fix. Now, when the StreamingContext.stop() is called, the following sequence of steps will happen.
1. The driver will send a stop signal to all the active receivers.
2. Each receiver, when it gets a stop signal from the driver, first stop receiving more data, then waits for the thread that persists data blocks to BlockManager to finish persisting all receive data, and finally quits.
3. After all the receivers have stopped, the driver will wait for the Job Generator and Job Scheduler to finish processing all the received data.

It also fixes the semantics of StreamingContext.start and stop. It will throw appropriate errors and warnings if stop() is called before start(), stop() is called twice, etc.

Author: Tathagata Das <tathagata.das1565@gmail.com>

Closes #247 from tdas/graceful-shutdown and squashes the following commits:

61c0016 [Tathagata Das] Updated MIMA binary check excludes.
ae1d39b [Tathagata Das] Merge remote-tracking branch 'apache-github/master' into graceful-shutdown
6b59cfc [Tathagata Das] Minor changes based on Andrew's comment on PR.
d0b8d65 [Tathagata Das] Reduced time taken by graceful shutdown unit test.
f55bc67 [Tathagata Das] Fix scalastyle
c69b3a7 [Tathagata Das] Updates based on Patrick's comments.
c43b8ae [Tathagata Das] Added graceful shutdown to Spark Streaming.