Add a .gitattributes file to handle Unix file on Windows

We like to keep the LF line endings, instead of changing to CRLF
Change file after uploading from a Windows hosts to LF

We have to change the line endings from CRLF to LF, just removing all CR
characters.  If you don't do that, the IPv4 address will not set for the
network interfaces.
Turn SERIAL option OFF by default

This option doesn't work on Windows 7 host at all. And leads to 100% CPU
usage on a Mac OSX 10.9 host.
Switch on VB.GUI by default and add some more customizing parameters for VirtualBox

Without vb.gui=true the VMs on a Windows 7 and Mac OSX 10.9 host didn't
start (tested with VirtualBox 4.3.10 and Vagrant 1.5.3)