Prepare for enabling H302 rule (api/volume,tempest/*)

We can use H302 rule but ignore it now. This commit prepares for
enabling H302 rule. But this commit modifies a part of Tempest only
because if we fix all of them at one time, it's hard to merge this
commit.
    ---------------
    tempest/api/compute/admin
    tempest/api/compute/{c*,f*,i*,s*,t*}
    tempest/api/compute/{v3,volumes},data_processing
    tempest/api/identity/admin
    tempest/api/image
    tempest/api/{n*,o*,t*}
    tempest/api/volume,tempest/*     <- This patch
    tempest/services/compute/json
    tempest/services/compute/v3/json
    tempest/services/compute/xml
    tempest/services/identity
    tempest/services/{im*,n*,o*,t*}
    tempest/services/volume
    tempest/clients.py: TBD
    ---------------

Change-Id: I65e9ac5678d17f31de5449017f2193f53c74c535
diff --git a/tempest/common/rest_client.py b/tempest/common/rest_client.py
index 03dccd4..66b6fe7 100644
--- a/tempest/common/rest_client.py
+++ b/tempest/common/rest_client.py
@@ -25,7 +25,7 @@
 from tempest import config
 from tempest import exceptions
 from tempest.openstack.common import log as logging
-from tempest.services.compute.xml.common import xml_to_json
+from tempest.services.compute.xml import common
 
 CONF = config.CONF
 
@@ -299,11 +299,11 @@
                 # Parse list-like xmls (users, roles, etc)
                 array = []
                 for child in element.getchildren():
-                    array.append(xml_to_json(child))
+                    array.append(common.xml_to_json(child))
                 return array
 
             # Parse one-item-like xmls (user, role, etc)
-            return xml_to_json(element)
+            return common.xml_to_json(element)
 
     def response_checker(self, method, url, headers, body, resp, resp_body):
         if (resp.status in set((204, 205, 304)) or resp.status < 200 or