update get_num_remaining_mutations for new build
update get_num_remaining_mutations for new build

Change-Id: Iaaddef07cbeb58e1da14cebfdf147b391d93c02b
Reviewed-on: http://review.couchbase.org/c/perfrunner/+/144392
Tested-by: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: <7c5437523872fffef04ef9d4aaffcc0ca27fba16@gmail.com>

couchbase/perfrunner,couchbase/perfrunner,couchbase/perfrunner,couchbase/perfrunner,couchbase/perfrunner,couchbase/perfrunner