newvm: Configure serial console log file

When a VM uses a serial port for its default console, kernel messages
(e.g. panics) are lost if no console client is connected at the time.
This is a major disadvantage when compared to a graphical console, which
usually at least keeps a "screenshot" of the console when the kernel
crashes.

While researching the available console device types to determine how
best to implement a tool that would both log the output from the serial
console at all times, while still allowing interactive connections to
it, I discovered that _libvirt_ actually already has this exact
functionality built-in:

https://libvirt.org/formatdomain.html#consoles-serial-parallel-channel-devices

newvm.sh

@@ -128,6 +128,7 @@ set -- \
     --disk pool=default,size=${disk_size},cache=none \
     --network ${network} \
     --os-variant fedora$(rpm -E %fedora) \
+    --console pty,target.type=serial,log.file=/var/log/libvirt/console/${name}.log \
     --sound none \
     --redirdev none \
     --rng /dev/random \