Various cleanups and warning fixes.

Particularly interesting is the change to ZooKeeperUpdatingPersistentDirectory.
I have no idea if that ever worked, as if it ever removed a node, it would get
a ConcurrentModificationException.
Reset joda-time to use system clock after test.

This would actually have a chance to affect other tests later on,
e.g. the ExpiredJobReaperTest which also depends on now()
Merge pull request #212 from mbruggmann/fix-now-in-grace-test

Reset joda-time to use system clock after test.
Add failing test case for container termination
Stop containers instead of killing them.
Only run the TerminationTest if docker runs the native driver.
Merge pull request #207 from dflemstr/termination

Stop running containers instead of killing them on undeploy
Merge pull request #211 from spotify/drewc/cleanups

Various cleanups and warning fixes.
Remove some system time dependencies

Either remove the use of the clock altogether where it was
unnecessary, or refactor things to use a Clock interface
for controlling time.