MDL-53401 auth_mnet: add user created event trigger on MNET

Moodle does not fire user_created event while creating user via MNET.
That makes impossible to hook on user creation when user land into a host via MNET for the 1st time.

auth/mnet/auth.php

@@ -302,7 +302,7 @@ class auth_plugin_mnet extends auth_plugin_base {
             $remoteuser->firstaccess = 0;
             $remoteuser->confirmed = 1;
 
-            $remoteuser->id = $DB->insert_record('user', $remoteuser);
+            $remoteuser->id = user_create_user($remoteuser, false);
             $firsttime = true;
             $localuser = $remoteuser;
         }