virt-libvirt: Add libvirt_xml nested accessor generator

Signed-off-by: Chris Evich <cevich@redhat.com>
virt-libvirt: attach/detach device test

Signed-off-by: Chris Evich <cevich@redhat.com>
virt-libvirt: Remove disused VM methods

Signed-off-by: Chris Evich <cevich@redhat.com>
virt-libvirt: Fixup some unittest whitespace

Signed-off-by: Chris Evich <cevich@redhat.com>
fixup! virt-libvirt: attach/detach device test

Signed-off-by: Chris Evich <cevich@redhat.com>
fixup! virt-libvirt: attach/detach device test

Signed-off-by: Chris Evich <cevich@redhat.com>
virt-libvirt: Implement libvirt_xml.devices.disk

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