Move wait_for_maxscale functionality inside MaxScale

By exposing a (currently undocumented) debug endpoint that lets one
monitor interval pass, we make the reuse of the monitor waiting
functionality a lot easier. With it, when MaxScale is started by the test
framework it knows that at least one monitor interval will have passed for
all monitors and that the system is ready to accept queries.

maxscale-system-test/testconnections.cpp

@@ -724,7 +724,8 @@ void TestConnections::init_maxscale(int m)
                           "cp maxscale.cnf %s;"
                           "iptables -F INPUT;"
                           "rm -rf %s/*.log /tmp/core* /dev/shm/* /var/lib/maxscale/maxscale.cnf.d/ /var/lib/maxscale/*;"
-                          "%s",
+                          "%s"
+                          "maxctrl api get maxscale/debug/monitor_wait",
                           maxscales->maxscale_cnf[m],
                           maxscales->maxscale_log_dir[m],
                           maxscale::start ? "service maxscale restart;" : "");