Use module-style parameters with monitors

The common monitor parameters are now stored as module-style
parameters. This makes the error reporting as well as the type checks for
the parameters consistent with parameters declared by the modules.

server/core/test/test_modulecmd.cc

@@ -407,7 +407,7 @@ int test_domain_matching(const char* actual_module,
     /** Create a monitor */
     char *libdir = MXS_STRDUP_A("../../modules/monitor/mariadbmon/");
     set_libdir(libdir);
-    monitor_create(name, actual_module);
+    monitor_create(name, actual_module, NULL);
 
     const MODULECMD *cmd;