Added a mongrel2 based Dockerfile
Cleanups for automatic build
o Remove greenery submodule; install via pip instead
o Auto-correct conflicts with Vagrant image port redirection
o Updated docker.io cpppo/* Docker images
Improve Vagrant and Docker support
o Move Vagrantfile, and support Docker on both Ubuntu and Debian
o Improve clone/build procedure for cpppo/mongrel2, and add pymodbus
Reduce size of Docker images by cleaning APT cache after upgrade/install
Merge branch 'feature-mongrel2'