Add improved Dockerfile with wrapper script for seamless upgrades
Pull the newest image before running Twister from the remote docker image
Rename `docker-container` script to `twister-on-docker`
[docker] Use twisterd commandline as ENTRYPOINT instead of CMD

- allows running the container with additional command line parameters
Merge pull request #203 from djmaze/docker-integration

Add improved Dockerfile with wrapper script for seamless upgrades