vagrant: Make landrush optional

It's not packaged for Fedora right now, I'm using Atomic Workstation
where I'm trying to minimize stuff installed on the host, and finally
even if I did run it, I use dnsmasq for the whole system, plus libvirt
already uses dnsmasq, so networking gets super complicated with
another resolver.

This will make it easier for me to hack on this for now...I'll
probably investigate landrush at some point though.