Should we use a more generic transport for _detect_gce_environment()

[dhermes]

The current source uses the core httplib / http.client machinery to get the info.

1. The original reason we used the low-level library is because the timeout in httplib2 was taking too long. This may no longer be an issue, i.e. if the GCE check is the last one
2. It should probably use oauth2client.contrib._metadata utils

I'm filing this because after #586 all requests (except for this one) are "guaranteed" to pass through the transport.request method

[theacodes]

Yes. Let's.