Add a helper tool which clears zookeeper test dirs

Create a tool that can clear any leftover garbage left
by the testing of taskflow unit tests with zookeeper for
when this is needed (for example, a test does not clean up
correctly on its own).

Change-Id: Icfaf28273b76a6ca27683d174f111fba2858f055
Merge "Add a helper tool which clears zookeeper test dirs"