[WIP] More configuration options for networks

[inercia]

This PR does some cleanups in the libvirt_network block, adds some sub-blocks like dns {}, dhcp {} and includes new attributes like routes = []

[kayila]

I would like to see this also provide options to configure the parameters required for pxe booting. Specifically, the ability to provide a bootp parameter for the dhcp server and a tftp element. Can those be added? I don't mind adding them myself if people are interested.

[Bischoff]

Any hope to get this merged soon?

I need to be able to set up private networks without DHCP and DNS servers provided by libvirt.

[MalloZup]

i am currently splitting this big pr in smaller one, plus checking if it working. currently working on dhcp part one.