Fix Fog mocking

What does this MR do?

Fixes broken master introduced by https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/18855.

It is dependent on the state of Fog.mock?.

Does this MR meet the acceptance criteria?

• Conform by the code review guidelines
  • Has been reviewed by a Backend maintainer

What are the relevant issue numbers?

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/47300