vol: attach2 must always return with VOL_LOCK held

vol: attach2 must always return with VOL_LOCK held

attach2() is required to return with the VOL_LOCK held
even though it is called without it.  This must be true
for error conditions as well.  Not all error paths are
obtaining the VOL_LOCK before returning.  Add out paths for
lock held and lock unheld error cases.

(cherry picked from commit 58901738ad6280d0777dd8e77f8c09cc45da04bc)
Reviewed-on: http://gerrit.openafs.org/3177
Tested-by: Derrick Brashear <shadow@dementia.org>
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Change-Id: I6918987cd784e4e550c2525b537bda290dbacae8
Reviewed-on: http://gerrit.openafs.org/3221
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>