rgw: fix failed to create bucket if a non-master zonegroup has a single zone

rgw: fix failed to create bucket if a non-master zonegroup has a single zone

If a non-master zonegroup has a single zone, the metadata sync thread not running and
the non-master zonegroup can't sync user from master zonegroup,
so we can't create bucket(or other metadata update) in it
because the authenticated user not found in the zone of non-master zonegroup.

Signed-off-by: weiqiaomiao <wei.qiaomiao@zte.com.cn>
(cherry picked from commit 949af79b21098e6410bc29274cf36eae2d89faea)

Conflicts:
        src/rgw/rgw_rados.cc - retain d32654b7cd60ccc4e23d3f05b9e4385a697bacd6
            which was merged after this commit