Refactor repl_bucket_types test to eliminate race condition and reduce code duplication

* Refactor the repl_bucket_types test to elminate a race condition in cluster setup and reduce code duplication.
*  Fix problem with repl_util:wait_until_leader_converge function
    * The wait_until_leader_converge function could incorrectly return success if all of the results from the get_leader rpc calls were either undefined or all returned a badrpc tuple. In either case the particular result ends up as the sole unique value in a list and the success condition is verifying that the list is of length 1 regardless of the value of the member of the list. Change the function to filter the list of results for values that indicate failure prior to the success condition checking.