Support inter instance networking

[markdryan]

https://gist.github.com/mcastelino/88195a7d99811a177f5e643d1465e19e

[mcastelino]

@markdryan I will try and add this when I get time. In short this is what I plan to do

1. Create a systemd service that runs dnsmasq listening on the multicast group
2. Add a cli option to join a given network

For now I will add support for a single default network. So a ccloudvm can be either part of the default network or standalone.

Later we can add support for creating multiple networks.

• The SLIRP network will have the default route
• The VM Network is only for inter VM communication

Open: Do I need to add a firewall rule that prevents traffic from the VM network exiting the host if routing is enabled.