Docker based build for b2d box

Hi !

This PR change the build process, taking advantages of docker trusted build for boot2docker, and using the brand new Vagrant 1.6 Docker provider.

The new build will inject ./vagrant script (the one put on /etc/rc.d by the build-iso script) during Dockerbuild : no need to get a heavy ubuntu, download dependencies as lzma, and using CPU for opening/closing the iso => It'll improve the build speed.

Otherwise, 
* Doc has been updated (little bit)
* Headless option has been added for vbox provider in packer, for building from an IC system.
* The Vagrantfile template, pushed into the box during packer build, has been updated for managing auto_config port for Docker TCP socket (cases when docker daemon is running in TCP mode on the Host AND we want to launch b2d box => it avoid collisions).