chore(registry): bump version to v0.8.1
test(registry): remove unit tests

the unit tests are outdated, useless and consistently failing. We were
cloning and running the unit tests correctly some months ago, but now
it requires a local redis. Unit tests are covered by
docker/docker-registry, anyways.
ref(tests/etcdutils): optimize test-etcd Dockerfile

Reduces the virtual size of "deis/test-etcd" from 467.4MB to 200.8MB.