Ignore .vagrant/

Signed-off-by: Gianpaolo Macario <gianpaolo_macario@mentor.com>
Vagrantfile: A few changes

To make it work in the following configuration:
* OS: MS Windows 7 64-bit
* VirtualBox 4.3.10
* Vagrant 1.5.4

TODO: Split into separate commits with proper documentation.

Signed-off-by: Gianpaolo Macario <gianpaolo_macario@mentor.com>
Update README.md