use sync. client for reb+xdcr

Change-Id: Id2da56ba298ea3fe868914861ef8ec81c7231ab6
Reviewed-on: http://review.couchbase.org/38945
Reviewed-by: Pavel Paulau <pavel.paulau@gmail.com>
Tested-by: Pavel Paulau <pavel.paulau@gmail.com>
tune number of workers

Change-Id: I6555a43f722477dd6abb392bfe3b5e97a36f01a9
Reviewed-on: http://review.couchbase.org/38946
Reviewed-by: Pavel Paulau <pavel.paulau@gmail.com>
Tested-by: Pavel Paulau <pavel.paulau@gmail.com>