Lock detach_volume
Lock detach_volume

A detach_volume operation may take place during a attach_volume or
delete_instance opertaion. This may lead to a race condition which
would result in an instance going into an error state as the volume
operation is not atomic.

Commit 4c4dc3a6d added the lock around the attach_volume. This
follows that same pattern.

Co-Authored-By: Matthew Booth <mbooth@redhat.com>

Change-Id: I7261135a44f0c2eca4732c8360b9c74b729991a8
Closes-bug: #1662483

rahulunair/nova,klmitch/nova,mahak/nova,mahak/nova,rahulunair/nova,klmitch/nova,openstack/nova,mahak/nova,rahulunair/nova,klmitch/nova,klmitch/nova,openstack/nova,openstack/nova