[EDP] Refactor the job manager unit tests around job engines

The job manager has been refactored to support multiple EDP engines (the newest of which is the Spark engine)

The job manager unit tests should be refactored as follows

* subdirectory for each EDP engine type (spark subdir added as part of the Spark EDP change request)
* job manager common utils at the top level

This essentially involves moving the unit tests for the Oozie implementation into a subdirectory, extracting Oozie-specific tests from the current test_job_manager.py and leaving only tests common to all engines at the top level

(spec in progress)