Port of mk-validate-username-change-with-container-registry-tags to EE
Port of mk-validate-username-change-with-container-registry-tags to EE
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/13356
Port of mk-validate-username-change-with-container-registry-tags to EE
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/13356