vol: Pay attention to specialStatus after VAVByVp

vol: Pay attention to specialStatus after VAVByVp

attach2/VAttachVolumeByVp_r do not alter the yielded error code
according to specialStatus. So, pay attention to specialStatus after
receiving an error from VAttachVolumeByVp_r, to ensure we respond with
the correct error code.

Reviewed-on: http://gerrit.openafs.org/7303
Reviewed-by: Tom Keiser <tkeiser@sinenomine.net>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>
(cherry picked from commit a81f9237bfa7b2e3a0567a930f3c49234b9a4376)

Change-Id: I1d0cb429b9cd875fa43a3af2e8c5d5d96ee12f85
Reviewed-on: http://gerrit.openafs.org/7491
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>