Trying to increase configurability

Hello,

I recently had to satisfy the need for a configurable Devstack deployment and your cookbook was the best starting point.

In order to increase its configurability, I introduced the `node[:devstack][:localrc]` attribute "namespace" that is handed through to the `localrc` file used by Devstack. (I added a `Vagrantfile` to illustrate its usage.)

It should be backwards-compatible (see `attributes/default.rb`), but I'm not 100% sure about this (increased the version, hope you don't mind).

Cheers
Stephan