xml_to_json should not convert xmlns into attribute

We should not treat xmlns as json payload.

Fixes LP# 1152630

Change-Id: Ib30759d0b6782b70356b4aa057227c01a2306fee
diff --git a/tempest/services/compute/xml/common.py b/tempest/services/compute/xml/common.py
index bbc4e38..4b1b11a 100644
--- a/tempest/services/compute/xml/common.py
+++ b/tempest/services/compute/xml/common.py
@@ -100,7 +100,8 @@
     """
     json = {}
     for attr in node.keys():
-        json[attr] = node.get(attr)
+        if not attr.startswith("xmlns"):
+            json[attr] = node.get(attr)
     if not node.getchildren():
         return node.text or json
     for child in node.getchildren():