DAFS: Do not attach a specialStatus'd vol

DAFS: Do not attach a specialStatus'd vol

If we encounter a preattached volume during GetVolume, we currently
ignore vp->specialStatus before trying to attach. However, we will
generally always fail to attach due to a conflicting vol op, but even
if we don't, GetVolume always returns an error later on if
vp->specialStatus is set. So, same some processing and attempted
attachments by bailing out sooner if vp->specialStatus is set.

Reviewed-on: http://gerrit.openafs.org/4874
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit f5349051abebd15fc2f2d77ff5b6dc81e09bdf47)

Change-Id: I3593a50b5867c671fe462abd40b50dcbbd2c5204
Reviewed-on: http://gerrit.openafs.org/4945
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>