move master db compaction to the separate scheduler

this will make furter redesign of kv compaction less confusing

Change-Id: Ifef8aadaf914efe6088b12e2e969864914469fcd
Reviewed-on: http://review.couchbase.org/39557
Tested-by: Artem Stemkovski <artem@couchbase.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>