Wait for monitor in mxs1719

Replaced hard-coded sleep with dynamic waiting.

maxscale-system-test/mxs1719.cpp

@@ -75,8 +75,7 @@ int main(int argc, char* argv[])
     {
         if (test.maxscales->start() == 0)
         {
-            // Give the monitor a few seconds to monitor the servers
-            sleep(5);
+            test.maxscales->wait_for_monitor();
 
             if (test.maxscales->connect_rwsplit() == 0)
             {