The new metrics is:

  cloudprovider_gce_api_request_duration_seconds{request, region, zone}
  cloudprovider_gce_api_request_errors{request, region, zone}

`request` is the specific function that is used.
`region` is the target region (Will be "<n/a>" if not applicable)
`zone` is the target zone (Will be "<n/a>" if not applicable)

Note: this fixes some issues with the previous implementation of
metrics for disks:
- Time duration tracked was of the initial API call, not the entire
  operation.
- Metrics label tuple would have resulted in many independent
  histograms stored, one for each disk. (Did not aggregate well).