Enable multiattach capability for the VMAX driver for Cinder

Support multiattach capability with Dell EMC VMAX arrays.

Allow retyping of replicated volumes - enabling and disabling - in VMAX driver for Cinder

The proposed feature would allow a user to retype a non-replicated volume to a replication-enabled volume type (enabling replication on that volume); from one replication-enabled type to another; and from a replicated volume type to a non-replicated volume type (disabling replication on that volume).