Allow deleting instances while uuid lock is held

Avoid issues where locked up operations on the instance prevent it
from being deleted by the user. Reasons for the lock up are a separate
issue and will be handled elsewhere, but terminating the instance
should not affect any tasks anyway. Any modification should already
gracefully handle the instance going away.

For more discussion about the issue see:
http://lists.openstack.org/pipermail/openstack-dev/2013-October/017454.html

This patch was merged once before and had to be reverted in
6b7304d8d38c0f04643bdcd031d682c688c91b28.  It was causing an extremely
large number of errors in gate jobs.  I believe that the case being hit
should be expected with this patch in place, and that it's actually OK.
We expect that the rest of the code will handle this case gracefully.
Simply remove this error message from the code.

Change-Id: I83deae464518fef5abe8fc00bfd0a186de01527b
Partial-Bug: #1248563
Co-authored-by: Russell Bryant <rbryant@redhat.com>
Merge "Allow deleting instances while uuid lock is held"