qemu: Don't bother user with libvirt-internal paths

qemu: Don't bother user with libvirt-internal paths

If user defines a virtio channel with UNIX socket backend and doesn't
care about the path for the socket (e.g. qemu-agent channel), we still
generate it into the persistent XML.  Moreover when then user renames
the domain, due to its persistent socket path saved into the per-domain
directory, it will not start.  So let's forget about old generated paths
and also stop putting them into the persistent definition.

https://bugzilla.redhat.com/show_bug.cgi?id=1278068

Signed-off-by: Martin Kletzander <mkletzan@redhat.com>