test-runner: set env flag if valgrind is being used

If the hw.conf option 'start_iwd' is false, then iwd is started
inside the python test, which means it will not know if the
--valgrind option was passed to test runner. If this is the case
an environment variable is set so the python test knows the
option is being used.

tools/test-runner.c

@@ -1802,6 +1802,10 @@ static void create_network_and_run_tests(const void *key, void *value,
 
 		if (iwd_pid == -1)
 			goto exit_hostapd;
+	} else {
+		/* tells pytest to start iwd with valgrind */
+		if (valgrind)
+			setenv("IWD_TEST_VALGRIND", "on", true);
 	}
 
 	if (ofono_req) {