Test atomic.compare_exchange_strong

Change-Id: I86eddad2c39e30b222e73565d0dd491a5cbc5bc7
Reviewed-on: http://review.couchbase.org/31677
Reviewed-by: Chiyoung Seo <chiyoung@couchbase.com>
Tested-by: Chiyoung Seo <chiyoung@couchbase.com>