[google|compute] Refactor Compute to use the new Shared module

Commit d801b27 introduced a new Shared module with logic to initialize
a google_client_api and to make requests.

This commit refactors Compute to use the new Shared module.
Merge pull request #3080 from frodenas/gce_shared

[google|compute] Refactor Compute to use the new Shared module