make xml_to_json parsing consistent

[Aditi Raveesh]

The xml_to_json parsing strips out the namespace from the attributes of a node while constructing the json.
However, the namespace is retained in the key, if it is an attribute of the node in the xml.
We need to keep this consistent across both attributes and child elements in the xml.

For eg.
<flavor name="flavor_namespace:flavor_name">
      <extra_spec_namespace:extra_spec>value</extra_spec_namespace:extra_spec>
</flavor>

gets converted to json in this way:
{"name": "flavor_name", "extra_spec_namespace:extra_spec": "value"}
(Attribute's namespace is stripped off, but child element's namespace is retained)

[Mauro S M Rodrigues (maurorodrigues)]

the issue was fixed at tempest/services/compute/xml/flavors_client.py