Ubuntu upgrade fixes,
    1. stop rabbitmq and upgrade the rabbitmq-server pacakage as the start of rabbitmq fails in posinst script of rabbitmq-server due to mismatch in rabitmq version of clustered nodes.
    2. remove zookeeper from config nodes, it is not removed during upgrade of contrail-openstack-config as it is a recommended package for contrail-config.

Change-Id: Ie21c663c9c638f137d46c227a740c15068a0c313