JCBC-350: Avoide race condition in observe replica.

This changeset uses the locator only and avoids a possible
race condition where the config contains stale data that does
not correlate with the locator information.

This can lead to a possible IndexOutOfBounds exception down the
call stack.

Change-Id: I4dea46c96ce78f7aaccf6cfff6ecd0629aa19894
Reviewed-on: http://review.couchbase.org/28477
Reviewed-by: Michael Nitschinger <michael.nitschinger@couchbase.com>
Tested-by: Michael Nitschinger <michael.nitschinger@couchbase.com>