Do not wait, but check regularly

tests/applications/gnome-initial-setup/aaa_setup.pm

@@ -16,10 +16,10 @@ sub run {
     # Remove the user clear the system and force the gnome-initial-setup
     # to start on new boot.
     assert_script_run("loginctl kill-user $username");
-    # do nothing for 10 seconds to give the previous command finish correctly
-    sleep(10);
     # closing the user might switch us back to GDM, switch away if so
     $self->root_console(tty => 3) if (check_screen 'graphical_login', timeout => 30);
+    # check until all user processes are terminated, then proceed and delete the user
+    assert_script_run("for i in {1..30}; do ! pgrep -u $username >/dev/null && exit 0; sleep 1; done; pgrep -au $username; exit 1");
     assert_script_run("userdel -r $username");
 
     # Reboot the system to trigger GNOME initial setup