do not allow views and kv compaction interrupt each other too often

... becaused it can cause kv compaction near suffocation
kv compaction and view compaction can now be interrupted by throttle
only between buckets, not between individual files

Change-Id: I422833b5d3f80555911ecae65301fcd5e1cb055d
Reviewed-on: http://review.couchbase.org/39393
Tested-by: Artem Stemkovski <artem@couchbase.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>