Bug 60964 - Job#isBlocking doesn't work for all cases

Also consider waiting ThreadJobs in JobManager#isBlocking()

Change-Id: I26b19c4f1ea75ac9fd38405023d6b7fe0a9aacc1
Signed-off-by: Jan Koehnlein <jan.koehnlein@itemis.de>
Bug 60964 - Job#isBlocking doesn't work for all cases

Comment added to document the change.