[SPARK-6980] [CORE] Akka timeout exceptions indicate which conf controls them (RPC Layer)

Latest changes after refactoring to the RPC layer.  I rebased against trunk to make sure to get any recent changes since it had been a while.  I wasn't crazy about the name `ConfigureTimeout` and `RpcTimeout` seemed to fit better, but I'm open to suggestions!

I ran most of the tests and they pass, but others would get stuck with "WARN TaskSchedulerImpl: Initial job has not accepted any resources".  I think its just my machine, so I'd though I would push what I have anyway.

Still left to do:
* I only added a couple unit tests so far, there are probably some more cases to test
* Make sure all uses require a `RpcTimeout`
* Right now, both the `ask` and `Await.result` use the same timeout, should we differentiate between these in the TimeoutException message?
* I wrapped `Await.result` in `RpcTimeout`, should we also wrap `Await.ready`?
* Proper scoping of classes and methods

hardmettle, feel free to help out with any of these!

Author: Bryan Cutler <bjcutler@us.ibm.com>
Author: Harsh Gupta <harsh@Harshs-MacBook-Pro.local>
Author: BryanCutler <cutlerb@gmail.com>

Closes #6205 from BryanCutler/configTimeout-6980 and squashes the following commits:

46c8d48 [Bryan Cutler] [SPARK-6980] Changed RpcEnvSuite test to never reply instead of just sleeping, to avoid possible sync issues
06afa53 [Bryan Cutler] [SPARK-6980] RpcTimeout class extends Serializable, was causing error in MasterSuite
7bb70f1 [Bryan Cutler] Merge branch 'master' into configTimeout-6980
dbd5f73 [Bryan Cutler] [SPARK-6980] Changed RpcUtils askRpcTimeout and lookupRpcTimeout scope to private[spark] and improved deprecation warning msg
4e89c75 [Bryan Cutler] [SPARK-6980] Missed one usage of deprecated RpcUtils.askTimeout in YarnSchedulerBackend although it is not being used, and fixed SparkConfSuite UT to not use deprecated RpcUtils functions
6a1c50d [Bryan Cutler] [SPARK-6980] Minor cleanup of test case
7f4d78e [Bryan Cutler] [SPARK-6980] Fixed scala style checks
287059a [Bryan Cutler] [SPARK-6980] Removed extra import in AkkaRpcEnvSuite
3d8b1ff [Bryan Cutler] [SPARK-6980] Cleaned up imports in AkkaRpcEnvSuite
3a168c7 [Bryan Cutler] [SPARK-6980] Rewrote Akka RpcTimeout UTs in RpcEnvSuite
7636189 [Bryan Cutler] [SPARK-6980] Fixed call to askWithReply in DAGScheduler to use RpcTimeout - this was being compiled by auto-tupling and changing the message type of BlockManagerHeartbeat
be11c4e [Bryan Cutler] Merge branch 'master' into configTimeout-6980
039afed [Bryan Cutler] [SPARK-6980] Corrected import organization
218aa50 [Bryan Cutler] [SPARK-6980] Corrected issues from feedback
fadaf6f [Bryan Cutler] [SPARK-6980] Put back in deprecated RpcUtils askTimeout and lookupTimout to fix MiMa errors
fa6ed82 [Bryan Cutler] [SPARK-6980] Had to increase timeout on positive test case because a processor slowdown could trigger an Future TimeoutException
b05d449 [Bryan Cutler] [SPARK-6980] Changed constructor to use val duration instead of getter function, changed name of string property from conf to timeoutProp for consistency
c6cfd33 [Bryan Cutler] [SPARK-6980] Changed UT ask message timeout to explicitly intercept a SparkException
1394de6 [Bryan Cutler] [SPARK-6980] Moved MessagePrefix to createRpcTimeoutException directly
1517721 [Bryan Cutler] [SPARK-6980] RpcTimeout object scope should be private[spark]
2206b4d [Bryan Cutler] [SPARK-6980] Added unit test for ask then immediat awaitReply
1b9beab [Bryan Cutler] [SPARK-6980] Cleaned up import ordering
08f5afc [Bryan Cutler] [SPARK-6980] Added UT for constructing RpcTimeout with default value
d3754d1 [Bryan Cutler] [SPARK-6980] Added akkaConf to prevent dead letter logging
995d196 [Bryan Cutler] [SPARK-6980] Cleaned up import ordering, comments, spacing from PR feedback
7774d56 [Bryan Cutler] [SPARK-6980] Cleaned up UT imports
4351c48 [Bryan Cutler] [SPARK-6980] Added UT for addMessageIfTimeout, cleaned up UTs
1607a5f [Bryan Cutler] [SPARK-6980] Changed addMessageIfTimeout to PartialFunction, cleanup from PR comments
2f94095 [Bryan Cutler] [SPARK-6980] Added addMessageIfTimeout for when a Future is completed with TimeoutException
235919b [Bryan Cutler] [SPARK-6980] Resolved conflicts after master merge
c07d05c [Bryan Cutler] Merge branch 'master' into configTimeout-6980-tmp
b7fb99f [BryanCutler] Merge pull request #2 from hardmettle/configTimeoutUpdates_6980
4be3a8d [Harsh Gupta] Modifying loop condition to find property match
0ee5642 [Harsh Gupta] Changing the loop condition to halt at the first match in the property list for RpcEnv exception catch
f74064d [Harsh Gupta] Retrieving properties from property list using iterator and while loop instead of chained functions
a294569 [Bryan Cutler] [SPARK-6980] Added creation of RpcTimeout with Seq of property keys
23d2f26 [Bryan Cutler] [SPARK-6980] Fixed await result not being handled by RpcTimeout
49f9f04 [Bryan Cutler] [SPARK-6980] Minor cleanup and scala style fix
5b59a44 [Bryan Cutler] [SPARK-6980] Added some RpcTimeout unit tests
78a2c0a [Bryan Cutler] [SPARK-6980] Using RpcTimeout.awaitResult for future in AppClient now
97523e0 [Bryan Cutler] [SPARK-6980] Akka ask timeout description refactored to RPC layer