On Ubuntu: don't start Zookeeper twice
On Ubuntu: don't start Zookeeper twice

On Ubuntu, if the Zookeeper service is already running, attempting
to start it again fails with non-zero exit code. This patch detects
whether ZK is already started before trying to start it.

Change-Id: If1257152de01fe5fe0351fdbb538bce083edbec0
Closes-Bug: #1513741

prithivm/branch01,bswartz/devstack,group-policy/devstack,samgoon/devstack,group-policy/devstack,Mahito/devstack,dtroyer/devstack,varunarya10/devstack,dirkmueller/devstack,dtroyer/devstack,noironetworks/devstack,mssumanth/devstack,dirkmueller/devstack,samgoon/devstack,thomasem/devstack,bigswitch/devstack,noironetworks/devstack,richliu/devstack,bigswitch/devstack,mssumanth/devstack,Mahito/devstack,varunarya10/devstack,thomasem/devstack,avvocatodemarchis/devstack,nawawi/openstack,prithivm/branch01,bswartz/devstack,openstack-dev/devstack,richliu/devstack,openstack-dev/devstack,nawawi/openstack,avvocatodemarchis/devstack