Adding Dockerfile and instructions

This adds a Dockerfile that builds an image to compile cloudstack from source.
The container is based on ubuntu 14.04
The simulator is used
Mysql is package in the container and runs with jetty via supervisor

The build can take a long time as it downloads all packages, once cached it is much faster.

The Dockerfile can be optimized to reduce the image size, once done I will upload to Docker hub.

This can also make its way onto 4.4, 4.5 and master branch but the Marvin package version will need to be checked.

Instructions are added in the README