Update vagrantfile

Create development environment with Vagrant

Use the --dev option of install-site.sh so that
the existing git checkout is used.

Don't install gems in to the app directory in
development because this installs ~15K extra
files in to the VirtualBox share. VB has poor
performance when sharing directories containing
high file counts.

Share the host git checkout in to the VM

Update the Vagrantfile to API v2