MB-8383 Count {set,del}-return-meta in ops and xdcr_ops.

Change-Id: I2071876761438d8c91f635588cfa7d494bf614dd
Reviewed-on: http://review.couchbase.org/26649
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>