Disable replication_manager and fix mxs1323_stress false positive

The replication_manager is only designed for systems that have yum
installed which means it will always fail on non-RHEL/CentOS systems.

The query threads in mxs1323_stress were not checking whether the test had
ended while they were executing the queries. This caused test timeouts as
the queries can take a relatively long time.

maxscale-system-test/mxs1323_stress.cpp

@@ -16,7 +16,7 @@ void* async_query(void* data)
     {
         MYSQL* conn = test->open_rwsplit_connection();
 
-        for (int i = 0; i < 50; i++)
+        for (int i = 0; i < 50 && running && test->global_result == 0; i++)
         {
             const char* query = "SET @a = (SELECT SLEEP(1))";
             test->try_query(conn, query);