Running tests using a custom image does not use associated QA image

Description

When running tests against a custom image, not hosted on a Docker Hub, like registry.gitlab.com/gitlab-org/omnibus-gitlab/gitlab-ce:SHA it still tries to pull gitlab/gitlab-qa:SHA instead of registry.gitlab.com/gitlab-org/omnibus-gitlab/gitlab-qa:ce-SHA.

It makes it more difficult to test against a custom image locally.

Description to be extended.