Refactor repl_bucket_types test

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.
Merge branch 'refactor/repl_bucket_types'