Add option to configure devices in yaml file

Example:
tvheadend:
  image: tvheadend
  devices:
  - "/dev/dvb/adapter0/dvr0:/dev/dvb/adapter0/dvr0"

Format for each entry is HOST:CONTAINER.
If only HOST is given then the file will be the same
inside the container.
Note, this is actually a vendored version of http://github.com/docker/docker-py

These changes should be made upstream