rgw: fix handling of --remote in radosgw-admin period commands

[cbodley]

send_to_remote_gateway() was using RGWRados::zonegroup_conn_map and zone_conn_map to find a connection to the given --remote. the zone_conn_map only contains zones in the current zonegroup, however, so --remote didn't work for zones in other zonegroups

radosgw-admin period commit relies on send_to_remote_gateway() to commit the period to the master zone. if that master zone is another zonegroup, the command fails:

$ radosgw-admin period update --commit
Sending period to new master zone 2554ff93-3149-4e77-ab94-bfbff0493074
could not find connection for zone or zonegroup id: 2554ff93-3149-4e77-ab94-bfbff0493074
request failed: (2) No such file or directory
failed to commit period: (2) No such file or directory

Fixes: http://tracker.ceph.com/issues/19554

radosgw-admin period pull also uses send_to_remote_gateway(). because it no longer needs RGWRados::zone_conn_map for connections, the period pull command is now a raw_storage_op

[cbodley]

passed rgw suite: http://pulpito.ceph.com/cbodley-2017-04-10_19:26:19-rgw-wip-cbodley-testing---basic-mira/

[cbodley]

jenkins test this please

[cbodley]

ping @yehudasa @oritwas - this fix is needed to allow period commit from a secondary zonegroup

[oritwas]

@cbodley , is this tested in test_multi.py?

[cbodley]

@oritwas yes, when run with num_zonegroups=2, test_multi.py will fail to commit on the secondary zonegroup. with this fix, it succeeds

(pushed a rebase - there was a build failure from the recent change from atomic_t -> std::atomic that git didn't detect as a conflict)