Prepare the environment for running boot2docker on Windows, even behind corporate proxy.
Context: http://stackoverflow.com/a/29303930/6309
Set the environment variables and path for Git, Boot2Docker and VirtualBox.
Define aliases for VBoxManage (in order to expose ports on VirtualBox boot2docker vm easily)
The env.bat is supposed to be in the parent folder of the repo, in order to not been committed and pushed by mistake
(since it can include proxy environment vith username:password in it)