fix testapi test: libvlc_instance_(play|pause|stop) are asynchronous, so wait for them

src/control/testapi.c

@@ -256,6 +256,7 @@ static void test_media_player_play_stop(const char** argv, int argc)
 
     libvlc_media_instance_stop (mi, &ex);
     catch ();
+    sleep(1);
 
     libvlc_media_instance_release (mi);
     catch ();