DAFS: Ensure logging on attach2 errors

DAFS: Ensure logging on attach2 errors

The attach2 error path transitions a volume to VOL_STATE_ERROR, in
case whatever got us to that error path did not already put the volume
in an appropriate state. Log when we do this, to make sure we do not
end up with a volume in VOL_STATE_ERROR state silently.

Change-Id: I02c842b64882d96e707e867ee0f7730a2bebd405
Reviewed-on: http://gerrit.openafs.org/6168
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>