Fix non-interactive sudo test

`sudo -nv` can be used to verify whether the sudo command is prepared
to execute commands non-interactively, i.e. it will not ask for a
password.

If the password has already been cached by previous sudo commands, or
sudo is configured to give passwordless access, we can move on.
Otherwise, interactive sudo or lack of sudo access cannot be used to
run tests in an automated fashion.

tests/integration/pping_test.py

@@ -89,7 +89,7 @@ def test_pping_should_post_event_when_host_is_unreachable(
 def get_root_method():
     if os.geteuid() == 0:
         return []
-    elif os.system("sudo true") == 0:
+    elif os.system("sudo -nv") == 0:
         return ["sudo", "-E"]
     elif os.system("gosu root true") == 0:
         return ["gosu", "root"]