SPARK-1235: manage the DAGScheduler EventProcessActor with supervisor and refactor the DAGScheduler with Akka

https://spark-project.atlassian.net/browse/SPARK-1235

In the current implementation, the running job will hang if the DAGScheduler crashes for some reason (eventProcessActor throws exception in receive() )

The reason is that the actor will automatically restart when the exception is thrown during the running but is not captured properly (Akka behaviour), and the JobWaiters are still waiting there for the completion of the tasks

In this patch, I refactored the DAGScheduler with Akka and manage the eventProcessActor with supervisor, so that upon the failure of a eventProcessActor, the supervisor will terminate the EventProcessActor and close the SparkContext

thanks for @kayousterhout and @markhamstra to give the hints in JIRA

Author: CodingCat <zhunansjtu@gmail.com>
Author: Xiangrui Meng <meng@databricks.com>
Author: Nan Zhu <CodingCat@users.noreply.github.com>

Closes #186 from CodingCat/SPARK-1235 and squashes the following commits:

a7fb0ee [CodingCat] throw Exception on failure of creating DAG
124d82d [CodingCat] blocking the constructor until event actor is ready
baf2d38 [CodingCat] fix the issue brought by non-blocking actorOf
35c886a [CodingCat] fix bug
82d08b3 [CodingCat] calling actorOf on system to ensure it is blocking
310a579 [CodingCat] style fix
cd02d9a [Nan Zhu] small fix
561cfbc [CodingCat] recover doCheckpoint
c048d0e [CodingCat] call submitWaitingStages for every event
a9eea039 [CodingCat] address Matei's comments
ac878ab [CodingCat] typo fix
5d1636a [CodingCat] re-trigger the test.....
9dfb033 [CodingCat] remove unnecessary changes
a7a2a97 [CodingCat] add StageCancelled message
fdf3b17 [CodingCat] just to retrigger the test......
089bc2f [CodingCat] address andrew's comments
228f4b0 [CodingCat] address comments from Mark
b68c1c7 [CodingCat] refactor DAGScheduler with Akka
810efd8 [Xiangrui Meng] akka solution