[test-infra] Prevent "global name 'git' is not defined" error. (#1428)

This appears to be what was causing the manifest-generation step to fail on http://w3c-test.org/tools/runner/index.html

View on GitHub: https://github.com/w3c/web-platform-tests/pull/1428

Received on Friday, 28 November 2014 08:55:43 UTC