manager: do not set up signals in test mode

When we are running in test mode, we don't expect any signals.
In fact ^C should end the program. This also avoids permission
issues when running systemd-analyze verify.

src/core/manager.c

@@ -410,6 +410,9 @@ static int manager_setup_signals(Manager *m) {
 
         assert(m);
 
+        if (m->test_run)
+                return 0;
+
         assert_se(sigaction(SIGCHLD, &sa, NULL) == 0);
 
         /* We make liberal use of realtime signals here. On