Bincode doesn't support serde's deserialize_any, so it's easier to use
JSON for de/serializing events. Since they'll likely be pretty sparse,
the size difference shouldn't be a big deal.
Main changes:
* Use diesel instead of sled
* Split libvirt components into new crate, nzr-virt
* Start moving toward network-based cloud-init
To facilitate the latter, nzrdhcp is an added unicast-only DHCP server,
intended to be used behind a DHCP relay.
