A test for Exceptions thrown by Threads spawned by Task.call()

This PR adds a test of the exception handling when a Thread spawned by `Task.call()` throws a Exception. The test passes if that thriggers a `FailedTask` in the Driver that contains the thrown Exception as the (ultimate) cause.

This test invalidates the hypothesis for #908, as it currently passes.
Merge pull request #914 from Microsoft-CISL/weimer_rogueThreadTest

A test for Exceptions thrown by Threads spawned by Task.call()
Merge branch 'master' of github.com:Microsoft-CISL/REEF into sergiym_MLSS_netty4
Move REEFFileNames ahead of HADOOP classpath entries
Merge pull request #920 from dafrista/bcho_change_yarn_classpath

Move REEFFileNames ahead of HADOOP classpath entries
Merge branch 'master' of github.com:Microsoft-CISL/REEF into sergiym_MLSS_netty4