virt-libvirt: Accessor generators for common XML mods

Signed-off-by: Chris Evich <cevich@redhat.com>
virt-libvirt: Move libvirt_xml into a package

Signed-off-by: Chris Evich <cevich@redhat.com>
fixup! virt-libvirt: Move libvirt_xml into a package

Signed-off-by: Chris Evich <cevich@redhat.com>
virt-libvirt: Update libvirt_xml unittests

Signed-off-by: Chris Evich <cevich@redhat.com>
virt: Add reroot() method to xml_utils

Hide the 'private' name used by ElementTree._setroot() method and
that it will destroy the existing tree.  Simply make a backup
copy of the tree before re-rooting it at desired element.

Signed-off-by: Chris Evich <cevich@redhat.com>
virt-libvirt: Standardize libvirt_xml accessor method basics

Signed-off-by: Chris Evich <cevich@redhat.com>
virt-libvirt: Fully impliment libvirt Network XML

Signed-off-by: Chris Evich <cevich@redhat.com>