osd: Calculate degraded and misplaced more accurately

osd: Calculate degraded and misplaced more accurately

Calculate num_object_copies based on the larger of pool size,
up set size and acting set size.

Calculate num_objects_degraded as the difference between num_object_copies
and all copies found on acting set and backfilling up set OSDs.

Calculate num_objects_misplaced as all copies on acting set OSDs not in up set
less copies that have been backfilled to up set OSDs.

Fixes: http://tracker.ceph.com/issues/18619
Signed-off-by: David Zafman <dzafman@redhat.com>