CURATOR-141 Don't make calls to the client after PathChildrenCache has been closed.

The test case is a bit weird because it needed to intercept logging.
Also, I've added slf4j-log4j12 as a test dependency to control logging.
I think it should be added to the other poms as well, otherwise logging
seems to get lost.
CURATOR-141 Changed the way we detect a working log setup
Merge branch 'CURATOR-141' of https://github.com/karel1980/curator into CURATOR-141
CURATOR-141 - Reverted the logging additions to the pom.xml as they have already been covered by CURATOR-139