rgw: allow init complete to proceed in case of erroneus zone deletes

rgw: allow init complete to proceed in case of erroneus zone deletes

Currently a master zone delete in a zonegroup followed by a period commit would
render RGWRados to be unusable, check if the zonegroup is empty and continue
initialization in these cases so that removal can proceed.

Fixes: http://tracker.ceph.com/issues/37328
Signed-off-by: Abhishek Lekshmanan <abhishek@suse.com>
(cherry picked from commit 58eb3545e4db2c9208fbc09789b89dd9d2ff7a71)

*	src/rgw/services/svc_zone.cc
Changes are made to the same function in  rgw_rados.cc
as the rgw_rados refactor is post mimic