Add proper cluster testing scripts

The scripts start MaxScale processes on two different servers. The support
framework for the tests is in place but the tests themselves still need to
be modified to allow the use of non-localhost addresses.

maxscale-system-test/testconnections.h

@@ -338,7 +338,10 @@ public:
     static void require_galera_version(const char *version);
 
     /** Initialize multiple MaxScale instances */
-    void multiple_maxscales(bool value);
+    static void multiple_maxscales(bool value);
+
+    /** Set secondary MaxScale address */
+    static void set_secondary_maxscale(const char* ip_var, const char* ip6_var);
 
     /**
      * @brief add_result adds result to global_result and prints error message if result is not 0