Flatten request objects

[Javascript guide](https://cloud.google.com/compute/docs/api/javascript-guide) uses mixed request payload: w/ and w/o `resource` property. Empirically testing, it looks like in some cases `resource` property is not even considered, especially for `compute.instances.insert()`.

Unwrapping `resource` property into the request object always works. 
@marcacohen can you confirm? I know you've been using these elements.