DAFS: Do not VDeregisterVolOp_r while exclusive

DAFS: Do not VDeregisterVolOp_r while exclusive

We should wait for a volume to transition out of an exclusive state
before calling VDeregisterVolOp_r on a volume, since some code may be
examining the vol op outside of VOL_LOCK in an exclusive state. We
should be doing this anyway before performing volume state checks,
since we may be trying to e.g. attach the volume at the same time.

Change-Id: I3a5b78b7c0033887a973ce941ced592df8c4bf3d
Reviewed-on: http://gerrit.openafs.org/4287
Tested-by: Andrew Deason <adeason@sinenomine.net>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>