MB-8662: pass purge timestamp to couch compactor

Change-Id: I0936e91911417cb6018fac42e58beaaeac383aad
Reviewed-on: http://review.couchbase.org/27792
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
MB-8662: added REST API for setting purge interval

Change-Id: I787817e45e9c0550cc46fbaebd422d76a92f3da4
Reviewed-on: http://review.couchbase.org/27793
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>