Start stop containers 252

Not ready for review.
You can have internationalized domain names containing unicode characters, but they need to be encoded using the idna codec before passing them to DNS client libraries. @itamarst commented about that last week  when I marked a hostname as unicode (https://github.com/ClusterHQ/flocker/pull/232#discussion_r14667836) but I forgot to address that comment. For now I think it's probably safest to document and treat them as bytes and assume that they're already encoded. Ultimately, there should probably be a new `DomainName` type with the necessary encoding and decoding methods. I'll create a ticket now.