Inconsistent use of xml libraries

Most of the code base is using lxml.etree but there are a few places using xml.etree.ElementTree. We should be using a single library for xml processing:

vishvananda@firefly-2:~/cache/stack/nova (master)$ ack ElementTree
nova/image/s3.py
27:from xml.etree import ElementTree
191: manifest = ElementTree.fromstring(manifest)

nova/tests/api/ec2/test_middleware.py
30:from xml.etree import ElementTree
111: tree = ElementTree.fromstring(result.body)

nova/tests/fakelibvirt.py
17:from xml.etree import ElementTree
19: ParseError = ElementTree.ParseError
144: tree = ElementTree.fromstring(xml)
166: tree = ElementTree.fromstring(xml)
304: disk_info = _parse_disk_info(ElementTree.fromstring(xml))
310: disk_info = _parse_disk_info(ElementTree.fromstring(xml))
407: tree = ElementTree.fromstring(xml)
744: tree = ElementTree.fromstring(xml)

nova/tests/test_fakelibvirt.py
19:from xml.etree import ElementTree
255: ElementTree.fromstring(xml)
263: tree = ElementTree.fromstring(xml)
285: tree = ElementTree.fromstring(xml)
301: ElementTree.fromstring(conn.getCapabilities())

nova/tests/test_libvirt.py
26:from xml.etree import ElementTree
154: tree = ElementTree.fromstring(xml)
193: tree = ElementTree.fromstring(xml)
216: tree = ElementTree.fromstring(xml)
231: tree = ElementTree.fromstring(xml)
253: tree = ElementTree.fromstring(xml)
725: tree = ElementTree.fromstring(xml)
747: tree = ElementTree.fromstring(xml)
788: tree = ElementTree.fromstring(xml)
804: tree = ElementTree.fromstring(xml)
817: tree = ElementTree.fromstring(xml)
830: tree = ElementTree.fromstring(xml)
929: tree = ElementTree.fromstring(xml)
1387: tree = ElementTree.fromstring(xml)

nova/tests/test_libvirt_vif.py
17:from xml.etree import ElementTree
103: doc = ElementTree.fromstring(xml)
119: doc = ElementTree.fromstring(xml)
137: doc = ElementTree.fromstring(xml)
163: doc = ElementTree.fromstring(xml)

nova/tests/test_vsa.py
18:from xml.etree import ElementTree
163: elem = ElementTree.fromstring(user_data)

nova/virt/libvirt/connection.py
53:from xml.etree import ElementTree
492: doc = ElementTree.fromstring(xml)
500: return ElementTree.tostring(node)
550: doc = ElementTree.fromstring(xml)
630: domain = ElementTree.fromstring(xml_desc)
908: tree = ElementTree.fromstring(xml)
1463: doc = ElementTree.fromstring(domain.XMLDesc(0))
1486: doc = ElementTree.fromstring(xml)
1519: doc = ElementTree.fromstring(xml)
1677: xml = ElementTree.fromstring(xml)
2073: doc = ElementTree.fromstring(xml)

nova/volume/driver.py
25:from xml.etree import ElementTree
955: result_xml = ElementTree.fromstring(out)
981: result_xml = ElementTree.fromstring(out)

nova/volume/san.py
33:from xml.etree import ElementTree
454: result_xml = ElementTree.fromstring(out)
495: _xml = ElementTree.tostring(cluster_xml)

nova/vsa/utils.py
19:from xml.etree import ElementTree
27: SubElement = ElementTree.SubElement
29: e_vsa = ElementTree.Element("vsa")
79: _xml = ElementTree.tostring(e_vsa)