Before calling update_consistencygroup, a validation is done if volumes
are in valid states for action.
Divide the states allowed for adding and removing volumes from a CG,
and allow volume removal in states error and error_deleting.
Also added missing verification in manager update_consistencygroup in
case state has changed from cinder-api to cinder-volume.
Change-Id: I6f5fa8e9af67e17ab49e7f3423d4469640df790c
Closes-Bug: #1519377
