Use the instances/list API for GoogleComputeProvider.find() instead of instances/get

[mdwn]

According to https://cloud.google.com/compute/docs/api-rate-limits, Google Cloud's API rate limit is 20 requests/second. I noticed that, in GoogleComputeProvider.find(), the code currently iterates through the list of given IDs and gets one instance at a time. Given the API rate limit, this may be problematic. https://cloud.google.com/compute/docs/reference/latest/instances/list may be a better choice.

I realize that this may not be possible since list is a GET request only, or may be painful due to GET request sizes. Still, I think this is worth investigating.