The man page states that with --config the next boot is affected. This
can be understood as if _only_ the next boot was affected. This isn't
true if the machine is running.

This patch adds the full --live, --config, --current infrastructure and
tweaks stuff to correctly support the obsolete --persistent flag.

Note that this patch changes the the behavior of the --config flag to match the
use of this flag in rest of libvirt. This flag was mistakenly renamed from
--persistent that originaly had different semantics.