[FLOC-1031] Switch documentation to installing omnibus packages.

https://clusterhq.atlassian.net/browse/FLOC-1031
I guess it's just an incidental change.  And `mysql.Vagrantfile` is no longer used because we changed the documentation to use postgresql instead and made all of the examples use the same `Vagrantfile` which is `docs/gettingstarted/tutorial/Vagrantfile`?