Remove references to personally-maintained Vagrant boxes ("slowe/*"), replacing them with "bento/*" instead. Changes found in YAML/JSON data files as well as in some Vagrantfiles and in all applicable README files.
Signed-off-by: Scott Lowe <scott.lowe@scottlowe.org>
For KVM-based environments (which require nested virtualization support), update the README.md to note that VirtualBox is not supported. Also update the Vagrantfile for clearer indications that only VMware-based providers are supported.