I presume it is the missing Release file which is causing the problem. So in theory, #13 should resolve it, but I am raising this to track the two separately.
==> default: W
==> default: :
==> default: The repository 'http://teamcity.docker:8111/app/debrepo/TestRepoName01 xenial Release' does not have a Release file.
==> default: Reading package lists...
==> default: Building dependency tree...
==> default: Reading state information...
==> default: E
==> default: :
==> default: Unable to locate package tcDummyDeb