Support purging of working and release directories of build agents on a schedule

Attached patch for support

Patch looks good but haven't tried it yet.

My only comment is when build is executing or the release is on going, can you add a more descriptive log message instead of just saying that the "Build Agent is busy" or "Build Agent is executing a release" or "Unable to determine if Build Agent is executing a release."

If I saw that message, I would not know that the purge was not executed because the build agent is busy.

The log says:

Directory purge [directoryType=releases, daysOlder=0, retentionCount=0, deleteAll=false] not possible; Build Agent busy

I didn't see the "not possible" text earlier so I think that should be ok now

I think there should also be a notification in UI if unable to purge for some reason.

Currently, we still have to check the build agent logs to find out that the purge did not execute at all.

I was able to purge the working copies while currently preparing release.

Fixed the condition to determine if the build agent is currently executing a release.

Included the rollback queue and the checking if any (perform-release, prepare-release and rollback-release) of the executors is currently executing a task

Please disregard CONTINUUM-2658_2.patch, was not able to include the new classes.

Please use CONTINUUM-2658_3.patch instead for the fix on the release execution condition.

Filed CONTINUUM-2661 regarding UI notification for purge executions.

Patch applied in trunk r1162043. Thanks!

I also modified when checking if executing directory purge is allowed or not to make sure that we won't allow purging of working copies when release is ongoing.

added missing unit test in r1238919