This change ensures to call driver specific post-parse code to modify
domain definition after parsing hypervisor config the same way we do
after parsing XML.
Signed-off-by: NPavel Hrdina <phrdina@redhat.com>

Some of the LXC configuration properties aren't migrated since they
would only cause problems in libvirt-lxc:
  * lxc.network.ipv[46]: LXC driver doesn't setup IP address of guests,
    see rhbz#1059624
  * lxc.network.name, see rhbz#1059630

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

LXC rootfs can be either a directory or a block device or an image
file. The first two types have been implemented, but the image file is
still to be done since LXC auto-guesses the file format at mount time
and the LXC driver doesn't support the 'auto' format.

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.