volser: add more logs for failures during restore

volser: add more logs for failures during restore

In the current version of the volserver, some failures during volume
restores are not logged. In order to help debugging, this commit
introduces extra logs for possible failures during this process, so we
guarantee that an error at any point during the restore causes a
message to be logged.

Change-Id: I3647155aeb3f10316d9d7fecb5b126efc909f7b4
Reviewed-on: https://gerrit.openafs.org/13252
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Tested-by: BuildBot <buildbot@rampaginggeek.com>