Cannot make changes to the ATH image and its consumers in the same code change

[basil]

As of #1168, the ATH image used for a test run is not the same as the code under test (CUT), thereby breaking the ability to make changes to the ATH image and its consumers in the same code change. This effectively nullifies testing of changes to the ATH image. Rather the ATH image should be built once from the code under test (CUT) and then consumed from each of the parallel test branches.