Update quickstart instructions

* Recommend using a virtual environment
* Fix reference to multinode inventory
* Add explicit use of sudo where necessary
* Change ownership of /etc/kolla to current user

These changes should make it possible to copy/paste from the quickstart
to get a working deployment.

Change-Id: Ib3990f9e16eaa1e19a4ad5bfea5bdb2e4bc1c333