core: assume root always has a session for connection visibility

Normally, users which are not part of a login session can't access
connections.  Root won't always be part of a login session, so
allow root to bypass visibility checks.  The code already bypassed
the ACL checks for root, but in multiple places.  Consolidate those
checks into one function.

src/nm-manager-auth.c

@@ -512,6 +512,10 @@ nm_auth_uid_in_acl (NMConnection *connection,
 	g_return_val_if_fail (connection != NULL, FALSE);
 	g_return_val_if_fail (smon != NULL, FALSE);
 
+	/* Root gets a free pass */
+	if (0 == uid)
+		return TRUE;
+
 	s_con = nm_connection_get_setting_connection (connection);
 	g_assert (s_con);