MB-8966: correctly fetch global settings for XDCR UI

Previous code fetched global settings even before current replication
setting url is set.

Correct behavior is making sure we fetch both global and
per-replication settings every time we are refreshing it.

Change-Id: I02a715761bc0f9a4a8a42815c0f8befc454e3d9f
Reviewed-on: http://review.couchbase.org/28585
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>