machined: flush nscd caches whenever a machine comes/goes

This way, nss-mymachines should always serve authoritative data.

src/machine/machine.c

@@ -398,6 +398,7 @@ int machine_start(Machine *m, sd_bus_message *properties, sd_bus_error *error) {
         machine_save(m);
 
         machine_send_signal(m, true);
+        (void) manager_enqueue_nscd_cache_flush(m->manager);
 
         return 0;
 }
@@ -439,6 +440,7 @@ int machine_stop(Machine *m) {
         m->stopping = true;
 
         machine_save(m);
+        (void) manager_enqueue_nscd_cache_flush(m->manager);
 
         return r;
 }