firewalld integration

[bboozzoo]

Kind of related to #533. I use firewalld, which configures the traffic filtering rules via nftables, rather than iptables. Not stopping firewalld or forgetting to move the mpqemubr* interface to the right zone results in problems launching the instances. AFAIK libvirt integrates with firewalld by setting up a separate zone for the bridge interface.

[Saviq]

Hi @bboozzoo thanks for letting us know, we're going to be moving to LXD for our VM needs on Linux, so make sure they know about this requirement, too :)