Added vCenter option for Cinder Storage

When vCenter selected as a Hypervisor, the new 'vCenter'
option for Cinder is selected (DataStore using VMDK Driver).
Removed VMDK warning

Change-Id: I4827bfca02168cd5170194396e3a356408096546
Closes-Bug: #1359696
Merge "Added vCenter option for Cinder Storage"