mon/OSDMonitor: filter the added creating_pgs added from pgmap

mon/OSDMonitor: filter the added creating_pgs added from pgmap

the creating_pgs added from pgmap might contains pgs whose containing
pools have been deleted. this is fine with the PGMonitor, as it has the
updated pg mapping which is consistent with itself. but it does not work
with OSDMonitor's creating_pgs, whose pg mapping is calculated by
itself. so we need to filter the pgmap's creating_pgs when adding them to
OSDMonitor's creating_pgs with the latest osdmap.get_pools().

Fixes: http://tracker.ceph.com/issues/20067
Signed-off-by: Kefu Chai <kchai@redhat.com>