[google|compute] Complete Operations support

- Add missing Operation attributes
- Remove unnecessary attribute aliases
- Add "zone_name" attibute for backward compatibility
- Add "destroy" method for an Operation
- Add "all" method for Operations
- Fix a bug when building an empty response (ie on delete operations)
- Return nil on NotFound Operations (behave like other fog resources)
Merge pull request #2839 from frodenas/gce_operations

[google|compute] Complete Operations support