Use golden accounts for VCRs in tests

Created by: unknwon

In our current tests for communicating with code hosts, we do not have accounts that are made solely for producing VCRs, we need a conventional way to create and update VCRs. Otherwise it could cause big headache when someone else trying to update these VCRs in the future (i.e. restore what was there or make many unrelated changes to the PR).

This issue tracks the progress of:

1. Ensure we have set up stable sources for producing VCRs.
2. Check every place currently uses VCRs to use golden accounts.
   • repo-updater
   • authz provider
3. Update places where we should but haven't been using VCRs.

NOTE: Take a look at how newFixtures is used for Bitbucket Server client.