salvager: Give back volumes when exiting early

salvager: Give back volumes when exiting early

Sometimes the salvager exits a bit earlier than normal. For instance,
when no applicable inodes are found for a volume group, or if the
-inodes command line option was given. In these cases, we have already
checked out singleVolumeNumber from the fileserver (if we're salvaging
a single VG), so we need to give it back. So, give it back in those
instances.

Change-Id: I3ab732d3b640b76d3bdec7ac9d01e57dc5a54ade
Reviewed-on: http://gerrit.openafs.org/4297
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>