ubik: check if epoch is sane before db relabel

ubik: check if epoch is sane before db relabel

The sync-site relabels its database at the end of the first write
transaction. The new label will be equal to the time at which the
sync-site in question first received its coordinator mandate. This time
is stored by a global called ubik_epochTime. In order to make sure that
the new database label is sane, only relabel the database if
ubik_epochTime is within a specific range.

Reviewed-on: https://gerrit.openafs.org/12640
Reviewed-by: Mark Vitale <mvitale@sinenomine.net>
Reviewed-by: Andrew Deason <adeason@dson.org>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
(cherry picked from commit f5c289d00aaf7c5525b477da5b89f6675456c211)

Change-Id: I78ebd2b8aeae01ef5e3b826ad6f1de5a5c1db79e
Reviewed-on: https://gerrit.openafs.org/12886
Reviewed-by: Marcio Brito Barbosa <mbarbosa@sinenomine.net>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Mark Vitale <mvitale@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>