Assorted clean-up for Spark-on-YARN.

In particular when the HADOOP_CONF_DIR is not not specified.

Author: Patrick Wendell <pwendell@gmail.com>

Closes #488 from pwendell/hadoop-cleanup and squashes the following commits:

fe95f13 [Patrick Wendell] Changes based on Andrew's feeback
18d09c1 [Patrick Wendell] Review comments from Andrew
17929cc [Patrick Wendell] Assorted clean-up for Spark-on-YARN.
[Spark-1538] Fix SparkUI incorrectly hiding persisted RDDs

**Bug**: After the following command `sc.parallelize(1 to 1000).persist.map(_ + 1).count()` is run, the the persisted RDD is missing from the storage tab of the SparkUI.

**Cause**: The command creates two RDDs in one stage, a `ParallelCollectionRDD` and a `MappedRDD`. However, the existing StageInfo only keeps the RDDInfo of the last RDD associated with the stage (`MappedRDD`), and so all RDD information regarding the first RDD (`ParallelCollectionRDD`) is discarded. In this case, we persist the first RDD,  but the StorageTab doesn't know about this RDD because it is not encoded in the StageInfo.

**Fix**: Record information of all RDDs in StageInfo, instead of just the last RDD (i.e. `stage.rdd`). Since stage boundaries are marked by shuffle dependencies, the solution is to traverse the last RDD's dependency tree, visiting only ancestor RDDs related through a sequence of narrow dependencies.

---

This PR also moves RDDInfo to its own file, includes a few style fixes, and adds a unit test for constructing StageInfos.

Author: Andrew Or <andrewor14@gmail.com>

Closes #469 from andrewor14/storage-ui-fix and squashes the following commits:

07fc7f0 [Andrew Or] Add back comment that was accidentally removed (minor)
5d799fe [Andrew Or] Add comment to justify testing of getNarrowAncestors with cycles
9d0e2b8 [Andrew Or] Hide details of getNarrowAncestors from outsiders
d2bac8a [Andrew Or] Deal with cycles in RDD dependency graph + add extensive tests
2acb177 [Andrew Or] Move getNarrowAncestors to RDD.scala
bfe83f0 [Andrew Or] Backtrace RDD dependency tree to find all RDDs that belong to a Stage
[streaming][SPARK-1578] Removed requirement for TTL in StreamingContext.

Since shuffles and RDDs that are out of context are automatically cleaned by Spark core (using ContextCleaner) there is no need for setting the cleaner TTL while creating a StreamingContext.

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

Closes #491 from tdas/ttl-fix and squashes the following commits:

cf01dc7 [Tathagata Das] Removed requirement for TTL in StreamingContext.
[FIX: SPARK-1376] use --arg instead of --args in SparkSubmit to avoid warning messages

Even if users use `--arg`, `SparkSubmit` still uses `--args` for child args internally, which triggers a warning message that may confuse users:

~~~
--args is deprecated. Use --arg instead.
~~~

@sryza Does it look good to you?

Author: Xiangrui Meng <meng@databricks.com>

Closes #485 from mengxr/submit-arg and squashes the following commits:

5e1b9fe [Xiangrui Meng] update test
cebbeb7 [Xiangrui Meng] use --arg instead of --args in SparkSubmit to avoid warning messages
SPARK-1562 Fix visibility / annotation of Spark SQL APIs

Author: Michael Armbrust <michael@databricks.com>

Closes #489 from marmbrus/sqlDocFixes and squashes the following commits:

acee4f3 [Michael Armbrust] Fix visibility / annotation of Spark SQL APIs