dasalvager: unlink fsstate.dat when standalone

dasalvager: unlink fsstate.dat when standalone

If the DAFS salvager is running in a standalone mode, unlink the
fileserver's fsstate.dat file if any volumes change. Otherwise, volume
data could have changed and the fileserver will retain callback
promises for the data in those volumes until it tries to attach the
volume. This way, callbacks are broken via callback state
reinitialization.

A better solution is to record which volumes have changed, and the
fileserver can break callbacks for them on startup. But this at least
eliminates a regression from non-DAFS behavior.

Reviewed-on: http://gerrit.openafs.org/4638
Tested-by: Andrew Deason <adeason@sinenomine.net>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit 38efda16a2c5c9e74b5a23b5bdd2818a3353eec2)

Change-Id: Ic931ce8118e8d76d799ce7e731451a6a4bf3c241
Reviewed-on: http://gerrit.openafs.org/4662
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>