tests: put screenshots to ./logs by default

Logs is where we write all our custom test logs, let's also put the
screenshots in the same place by default from cluttering the base
directory.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Reviewed-by: Emilio Pozuelo Monfort <emilio.pozuelo@collabora.co.uk>
Reviewed-by: Micah Fedke <micah.fedke@collabora.co.uk>
Reviewed-by: Quentin Glidic <sardemff7+git@sardemff7.net>

tests/weston-test-client-helper.c

@@ -912,9 +912,10 @@ output_path(void)
 	char *path = getenv("WESTON_TEST_OUTPUT_PATH");
 
 	if (!path)
-		return ".";
+		return "./logs";
+
 	return path;
-	}
+}
 
 char*
 screenshot_output_filename(const char *basename, uint32_t seq)