osd: Reset() the snaptrimmer on shutdown

We were failing to exit various wait states which held PGRefs. Error!

Fixes: http://tracker.ceph.com/issues/19931

Signed-off-by: Greg Farnum <gfarnum@redhat.com>
(cherry picked from commit b0e9dee)

src/osd/PrimaryLogPG.cc

@@ -10136,6 +10136,8 @@ void PrimaryLogPG::on_shutdown()
   cancel_proxy_ops(false);
   apply_and_flush_repops(false);
   cancel_log_updates();
+  // clean up snap trim references
+  snap_trimmer_machine.process_event(Reset());
 
   pgbackend->on_change();