[google compute] adding Routes - redux

Replaces #400

This PR adds support for Google Compute Engine's Routes. This covers adding, listing, deleting, and fetching routes (all standard operations). The Routes API is here[1] and the GCE docs for routes are here[2]

Includes tests and new fixtures.

[1] https://cloud.google.com/compute/docs/reference/latest/routes
[2] https://cloud.google.com/compute/docs/networking#routing