support/misc: Adding Vagrant file for provisioning

This patch adds a Vagrant file to buildroot. With this file
you can provision a complete buildroot developing environment
in minutes on all major platforms (Linux/Mac/Windows).

[Peter: bump to 2GB RAM, hardcode Buildroot release, add unzip,
	drop website update and tweak manual text as suggested by Yann]
Signed-off-by: Angelo Compagnucci <angelo.compagnucci@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>