Sorry, I just noticed this - but is this assertion here (and elsewhere) superfluous?  Since `wait_for_active_list_in_group_state` won't return successfully anyway unless `active_server_list` == the expected number.

If you wanted to leave out the assertion, but still wanted to make it clear that `wait_for_active_list_in_group_state` was testing for the number of servers, perhaps the function could be named something more like `wait_for_expected_number_of_active_serves`, with parameter name `expected_servers`?