If the container is not found when removing, it means it's already not
there anymore, so it's safe to ignore. This should reduce a bit some
`TearDown` flakyness..
Signed-off-by: Vincent Demeester <vincent@sbr.pm>
This extract what was in registry_test.go and
registry_mock_test.go. This also move `RegistryHosting`
requirement to `registry.Hosting`
Signed-off-by: Vincent Demeester <vincent@sbr.pm>