[libvirt] Update on host interface configuration

[Itamar Heim]

> From: libvir-list-bounces at redhat.com [mailto:libvir-list-
> bounces at redhat.com] On Behalf Of David Lutterkort
...
> In particular, if you are part of the management system, you have a
> much
> better idea (on the node) what it means to have a working network
> configuration, and can recover from misconfigured network much more
> gracefully than with the big hammer of a system reboot.
[IH] indeed, but this implies the management system has to co-locate
another management daemon on the node, since central management cannot
rollback the node from an invalid network configuration. 
It will also be simpler for the other daemon to be the one accepting the
network change command from the central management, using libvirt locally
(or be notified by libvirt on BeforeNetworkChange/AfterNetworkChange  to
be able to backup conig, check for connectivity, and potentially only call
the rollback locally, so there won't be a need to implement the remote
management twice. 
another issue is that the change has to be treated as atomic for all
interfaces together, not one by one.