Leveling up my custom vagrant environment a bit.

Passing through the project directory's name as an arg to my provisioning
script (assumes Vagrantfile in top level of project directory). This is mainly
so I can use that info in the bash prompt via the PS1 variable (I'm the guy
with 15 terminal tabs open and I need some way to keep them straight and
colorizing the prompt ususally works for me).

Also adding multi-distro support (for now just Ubuntu/CentOS). Will extend
this as necessary if I bring up any FreeBSD, Fedora, etc. Vagrant boxes.