sync_repl.py: Add loop_set()
sync_repl.py: Add loop_set()

Add a loop_set() method which repeatedly calls set() on a single key;
and appending the iteration number to the value.

Update the existing loop_setD() method to set the value in the same
way.

Change-Id: Id0e5a6c060a4b8bc3ea3120c4ea6b4c3eebf953b
Reviewed-on: http://review.couchbase.org/103556
Tested-by: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: Paolo Cocchi <9dd88c9f3e5cbab6e19a6c020f107e0c648ac956@couchbase.com>

daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine