bos: allow salvage -salvagedirs with -all

bos: allow salvage -salvagedirs with -all

Allow the -salvagedirs option on bos salvage when invoked with the -all
option to salvage the whole server.   The -salvagedirs -all options will
rebuild every directory on the server.

Reviewed-on: https://gerrit.openafs.org/12457
Reviewed-by: Mark Vitale <mvitale@sinenomine.net>
Tested-by: Mark Vitale <mvitale@sinenomine.net>
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
(cherry picked from commit 1637c4d7c1ce407390f65509a3a1c764a0c06aa6)

[not actually cherry picked, but is the equivalent functionality]

Change-Id: I3978a5c4a704e0a0f2aab1cfad75573c16496a4d
Reviewed-on: https://gerrit.openafs.org/12462
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>