Use volumes for persistent storage

[hkumarmk]

Services like cassandra, zookeeper,etc need persistent storage which should be available from a volume or host directory mounted to the conatainers. This will benefit the performance, and any simple upgrade scenarios/any container resets (may be due to an error) as the data is not within the container.

[ramprackash]

Also, it would be good to have all the container logs (/var/log/contrail) on a volume from the host so it is easy to fetch and display all logs from one host.