[google|compute] Modify Flavors

- Add full "Machine Type" properties
- Replace deprecated "connection" for "service"
- Add "list_aggregated_machine_types" request
- Modify "all" method to return the full list of machine types (instead
  of the ones from the first zone)
Merge pull request #2847 from frodenas/gce_flavors

[google|compute] Bring Flavors model and related requests up to feature parity