Rename zookeeper_client to zk for nodepool.py
Rename zookeeper_client to zk for nodepool.py

Since we aren't actually using zookeeper_client, shorten the name to
zk.

Also fix a possible error in reconfigureZooKeeper() if we are using
multiple zookeeper-servers in our configuration.

Change-Id: I4104b91c7e11f340be533d1fcae8341a15087581
Signed-off-by: Paul Belanger <e7139c8e6c4ea75cc1c287ce081b2dc0f3ab39ec@redhat.com>

Tesora/tesora-nodepool,Tesora/tesora-nodepool