Enable some volumes v2 tests by sharing codes part2

1. Rename volumes v1 client to a base client, then create
   v1 and v2 clients inheriting base client.
2. create volumes v2 tests using the existent test class.
3. create a new test class for v1, which inherits v2.

This patch includes the following volumes tests:
- test_availability_zone.py
- test_extensions.py

Partially implements: blueprint cinder-v2-api-tests

Change-Id: Ie21ebc184710e9abe894cdc20ed7a39aacc94ded
diff --git a/tempest/api/volume/test_availability_zone.py b/tempest/api/volume/test_availability_zone.py
index fe8f96e..25b7b85 100644
--- a/tempest/api/volume/test_availability_zone.py
+++ b/tempest/api/volume/test_availability_zone.py
@@ -17,16 +17,15 @@
 from tempest import test
 
 
-class AvailabilityZoneTestJSON(base.BaseVolumeV1Test):
+class AvailabilityZoneV2TestJSON(base.BaseVolumeTest):
 
     """
-    Tests Availability Zone API List
+    Tests Availability Zone V2 API List
     """
-    _interface = 'json'
 
     @classmethod
     def setUpClass(cls):
-        super(AvailabilityZoneTestJSON, cls).setUpClass()
+        super(AvailabilityZoneV2TestJSON, cls).setUpClass()
         cls.client = cls.availability_zone_client
 
     @test.attr(type='gate')
@@ -37,5 +36,13 @@
         self.assertTrue(len(availability_zone) > 0)
 
 
-class AvailabilityZoneTestXML(AvailabilityZoneTestJSON):
+class AvailabilityZoneV2TestXML(AvailabilityZoneV2TestJSON):
+    _interface = 'xml'
+
+
+class AvailabilityZoneV1TestJSON(AvailabilityZoneV2TestJSON):
+    _api_version = 1
+
+
+class AvailabilityZoneV1TestXML(AvailabilityZoneV1TestJSON):
     _interface = 'xml'