OSD: handle the case where we resurrected an old, deleted pg

OSD: handle the case where we resurrected an old, deleted pg

Prior to giant, we would skip pgs in load_pgs which were not present in
the current osdmap.  Those pgs would eventually refer to very old
osdmaps, which we no longer have causing the assertion failure in 11429
once the osd is finally upgraded to a version which does not skip the
pgs.  Instead, if we do not have the map for the pg epoch, complain to
the osd log and skip the pg.

Fixes: 11429
Signed-off-by: Samuel Just <sjust@redhat.com>
(cherry picked from commit fbfd50de5b9b40d71d2e768418a8eca28b1afaca)

Conflicts:
	src/osd/OSD.cc
        resolved by add a new comment line