MB-9484: Allow upr to schedule backfills and send mutations/deleted

Change-Id: I1c8edf8f809626a56ff648c83799253c81a5410a
Reviewed-on: http://review.couchbase.org/30848
Reviewed-by: Chiyoung Seo <chiyoung@couchbase.com>
Tested-by: Chiyoung Seo <chiyoung@couchbase.com>