Standalone registry

It's now possible to push and pull on a standalone registry without configuring Docker (-registry argument has been removed).

```
# Pulling hipache from the official Registry
docker pull samalba/hipache
# Re-pushing it to my own Registry
docker push myregistry-shad.dotcloud.com/samalba/hipache
# It's also possible to push/pull on a local one (for dev?)
docker push localhost.localdomain:5000/samalba/hipache
```