Update qa/Dockerfile to be built from the project root context
See merge request gitlab-org/gitlab-ce!31533
(cherry picked from commit 4d4e88df01554336daf245a68653b80ca00989a5)
6aa215aa Support X_if_ee methods for QA tests
b601cfcf Update qa/Dockerfile to be built from the project root context
9a4dcd8d Update the 'build-qa-image' job to be built from project root context