Allow users to specify the master node in Vertica

[Mayuri Ganguly]

Currently in Vertica, the first node in the cluster is automatically chosen as the master node and the Management console is installed on it. but the user should be given the option to chose which node they want as the master node. They may be also able to specify the flavor size separately for the master node (currently, all the nodes in a cluster is identical). If the user does not specify a master node, then the master node should be automatically chosen.
The patch which modifies the Vertica cluster to have a master node is https://review.openstack.org/#/c/204271/34