osd/OSDMapMapping: fix spurious threadpool timeout errors

osd/OSDMapMapping: fix spurious threadpool timeout errors

We were passing a grace of zero seconds to our temporary work queue, which
led to the HeartbeatMap issuing cpu_tp timeout errors to the log.  By using
a non-zero grace period we can avoid these.  Use the same default grace
we use for the workqueue itself when it goes to sleep.

Fixes: https://tracker.ceph.com/issues/53506
Signed-off-by: Sage Weil <sage@newdream.net>
(cherry picked from commit 30ac5e79352839e285ec2eef6d603226d9071db4)