Add support for tags to docker build

- `docker build` now uses API instead of CLI
- You can now specify one or more tags to apply to an image. The default is `latest`.
- Check for SocketError when connecting to docker API and print more helpful message.
Add support for copying over data bags - fixes #27
Merge branch 'tduffield/FSE-105' into tduffield/1.0.0.rc.0
Merge branch 'tduffield/GH-27' into tduffield/1.0.0.rc.0