previous evaluators checking back in for driver HA
update recovery logic based on working 2.4.1 jar
add retained container in a more natural way and remove the need to add EvaluatorManager based on recovery heartbeat
add driver restart runningtask and activecontext handler
merge with master
add EvaluatorsChangeLog to HDFS, trigger failedEval when eval failed during driver restart, remove dependency on local file
close hdfs reader once done
Merge remote-tracking branch 'origin' into yingdac-evaluators-checking-back-in

Conflicts:
	reef-common/src/main/java/com/microsoft/reef/runtime/common/driver/evaluator/EvaluatorManager.java
Merge branch 'master' of https://github.com/Microsoft-CISL/REEF into yingdac-evaluators-checking-back-in
Minor updates
remove all static fields in evaluatormanager
fix other CR comments
Refactorings to reef-tests

This PR doesn't solve any specific issue, but instead does some code improvements to the REEF tests

  * Most tests now have a one-liner in the class JavaDoc as well as in `package-info.java`
  * Repetetive code (such as a driver start handler that requests a single evaluator) is moved to `c.m.reef.tests.library`
  * Most tests have had theit job renamed to start with `TEST_`
  * Classes with generic names such as `Driver` or `Task` have been renamed.

 Again, this PR contains *no functional changes*.
minor change in comment to trigger build
Merge pull request #967 from Microsoft-CISL/weimer_tests_cleanup

Refactorings to reef-tests
Merge branch 'master' of https://github.com/Microsoft-CISL/REEF into yingdac-evaluators-checking-back-in
State checks for `DriverStatusManager`
State checks for `DriverStatusManager`
Code pass through EvaluatorManager
Merge pull request #946 from Microsoft-CISL/yingdac-evaluators-checking-back-in

previous evaluators checking back in for driver HA