Cleanup onbuild docker file.
Fix issue with chmod not being able to run in onbuild
- now using python to launch the main file
Smart use of copy (requirements.txt* Dockerfile) to make sure we specific files in docker build process before copying all files. By using requirements.txt* Dockerfile we will make sure we always copy a file (Dockerfile) and the copy operation will not fail.
Added more documentation on how to use onbuild.