MB-8383 Count ret_meta commands as their ordinary counterparts.

And don't count them as xdcr ops.

Change-Id: Ic0eae1f5f9bdb95cfcb1ab78cb0ca22336c5ce0c
Reviewed-on: http://review.couchbase.org/26806
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>