Moved the test for RetainedEval to reef-tests

Closes #971

Also, this does some mild refactorings of the retained evaluators code base towards #928
Merge pull request #973 from Microsoft-CISL/weimer_971

Moved the test for RetainedEval to reef-tests.

Tests passed locally and on YARN (Windows)
Merge remote-tracking branch 'origin' into reef-bridge
allow user to set job submission directory
rename to DriverJobSubmissionDirectory
Merge branch 'yingdac-allow-setting-of-jobsubmissiondirectory' into reef-bridge
add jobsubmission directory
remove dup
update java doc
Merge branch 'yingdac-allow-setting-of-jobsubmissiondirectory' into reef-bridge
allow .net user to set driver job submission directory