Adjust log format
Expose salt ports
Use a volume for data storage

I moved the file and pillar root directory as well as the pki store to a data
volume mounted under /data. This keeps all persistent data in one place and
makes it easier to create a data-volume-only container for storing the data.
Make images suitable for connection with salt-shell

To be able to connect the image to a separate salt-shell image, which runs sshd
and makes it possible to execute salt commands in a different container, some
more directories had to be moved to the data volume. As well, the salt socket
directory and pid file have to be shared with the salt-shell.