CURATOR-42 - Modified guaranteed delete handling so that it will only
add the node to the guaranteed delete set if a recoverable exception is
encountered. If a non recoverable exception (such as a NoNodeException)
is encountered, then this will not be retried. Added a debug listener to
the FailedDeleteManager to facilitate unit testing this case. Added unit
tests, for both guaranteed deletes in the background and foreground for
the NoNodeException case. Note that this error was only present for
guaranteed deletes in the foreground.