Since kolla-mesos has been retired, there is no need in the code
base to keep the zookeeper implementation.  As a result, just remove
it.  If we were to keep it we need virtualenvs for that part of the
code base which installs the python dependencies related to it
for from-binary installs.

This just simplifies the implementation tremendously and culls dead
code.

Change-Id: Ieda226e652d67f5b5667112f4f2556f3171366d3
Closes-Bug: #1577194