vol: remove empty directories left by vos zap -force

vol: remove empty directories left by vos zap -force

The vos zap -force command does not remove the directories associated
with the volume in question (AFS_NAMEI_ENV). When the vos zap -force
command is executed, the volume server goes through the /vicep*/AFSIDat
directories and removes the files associated with the volume id received
as an argument. Unfortunately, the volume server does not remove the
directories associated with this volume. As a result, empty directories
are left behind.

To fix this problem, remove the empty directories left behind when vos
zap -force is executed.

Change-Id: I56fd52918223f87e424121bac6a086d7b0a46284
Reviewed-on: https://gerrit.openafs.org/12879
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Cheyenne Wills <cwills@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>