If no network configuration is provided, LXC only provides the loopback
interface. To match this, we need to use the privnet feature. LXC will
also define a 'none' network type in its 1.0.0 version that fits
libvirt LXC driver's default.

Tmpfs relative size and default 50% size values aren't supported as
we have no idea of the available memory at the conversion time.

This function aims at converting LXC configuration into a libvirt
domain XML description to help users migrate from LXC to libvirt.

Here is an example of how the lxc configuration works:
virsh -c lxc:/// domxml-from-native lxc-tools /var/lib/lxc/migrate_test/config

It is possible that some parts couldn't be properly mapped into a
domain XML fragment, so users should carefully review the result
before creating the domain.

fstab files in lxc.mount lines will need to be merged into the
configuration file as lxc.mount.entry.

As we can't know the amount of memory of the host, we have to set a
default value for max_balloon that users will probably want to adjust.