Merge pull request #9263 from @dezgeg.

This looks for the window title instead of OCRing the clock from the
IceWM panel. Of course, this has the drawback, that whenever IceWM is
started it doesn't necessarily mean that the panel is also visible at
that time, so we might want to drop the screenshot of the "session" as
well.

nixos/tests/lightdm.nix

@@ -22,7 +22,7 @@ import ./make-test.nix ({ pkgs, ...} : {
     $machine->waitForText(qr/${user.description}/);
     $machine->screenshot("lightdm");
     $machine->sendChars("${user.password}\n");
-    $machine->waitForText(qr/^\d{2}(?::\d{2}){2} (?:AM|PM)$/m);
+    $machine->waitForWindow("^IceWM ");
     $machine->screenshot("session");
   '';
 })