rgw: renew resharding locks to prevent expiration

rgw: renew resharding locks to prevent expiration

Fix lock expiration problem with resharding. The resharding process
will renew its bucket lock (and logshard lock if necessary) when half
the remaining time is left on the lock. If the lock is expired and
cannot renew the process fails and errors out appropriately.

Signed-off-by: J. Eric Ivancich <ivancich@redhat.com>