salvager: Do not AskOnline nonexistent volumes

salvager: Do not AskOnline nonexistent volumes

If singleVolumeNumber is not in our volume summary list, then the
singleVolumeNumber volume does not exist. So, don't try to bring it
back online. Still do try to make sure we don't have the volume
checked out, though, so issue an AskDelete, so ensure that it's not
checked out and that the fileserver does not think it exists.

Change AskDelete so we don't care if we tried to delete a volume that
the fileserver thinks already doesn't exist. Change the FSYNC_VOL_DONE
handler so it does not complain about already-deleted volumes.

Change-Id: I33dd876c0db91a3c8a5210fca329d63bf4b3d212
Reviewed-on: http://gerrit.openafs.org/4295
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>