virt: Add method to rebase an XML element to root

This is a convenience when you want some behavior to
only operate on a subtree of an XML document as if
it were a separate XML tree.

This functionality is provided by a 'private' name
in the ElementTree module to protect users from
some negative implications.  This method masks
those negative aspects and provides a public name.

Signed-off-by: Chris Evich <cevich@redhat.com>
virt: Small propcan module tweaks

* Updated docs

* Separated out Semi-private methods from PropcanBase class
  to reduce pylint noise coming from other modules.

* Changed __setitem__ to disallow setting properties not defined in
  __slots__ (as was original intention of class)

Signed-off-by: Chris Evich <cevich@redhat.com>
virt-libvirt: Package libvirt_xml w/ accessor generator

The module was growing too rapidly to be contained within a single
module and remain comprehensible.  Also The vast majority of
libvirt's XML can be operated on via a small collection of
common operations.  For example adding/removing a single tag
somewhere in the tree.

* Break libvirt_xml into a package, with submodules containing
  updated versions of the original classes.

* Impliment an accessor submodule to consolidates common
  operations into generator classes of callable subclass instances.

* The LibvirtXMLBase base-class is utilized by many subclasses
  soas to avoid circular dependencies, it was moved into its
  own 'base' module.

* All exception definitions would also have caused circular
  dependencies, so they were moved to a dedicated xcepts module.

* The LibvirtXML class (for working with 'capabilities') was
  moved into a  sub-module and updated to use the accessors module.

* The network_xml module now fully support all basic aspects of
  libvirt's host-network XML format.  It was updated extensivly
  to make use of common accessor methods.  New classes were added
  to help handle IP addresses and associated DHCP ranges for XML bridge
  description.

* The VMXML class was moved to the vm_xml module where it remains
  fairly basic/unchanged for now.  Becides converting classes to
  use the new accessor methods, little else was changed.

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

* Added new testcase class to test the accessors module

* Updated all classes to use package/submodules

* Updated all classes to use accessors module fully
virt-libvirt: Reapply dropped libvirt_xml patches

* 728416fb61b58a5a3e560ba61c298029c1709a3f
  virt-libvirt: fix bug in libvirt_xml
  杨东升 <yangds.fnst@cn.fujitsu.com>
  Thu Jan 10 14:43:48 2013 +0000

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