Add list roles api to identity v3

Identity v3 lack of list roles, so I do the addition.
To test the addition, I add a test in :
- test_role_create_update_get
and rename it :
- test_role_create_update_get_list

Change-Id: I1163df683ad16643773b3c75d895296c7e601b6b
diff --git a/tempest/api/identity/admin/v3/test_roles.py b/tempest/api/identity/admin/v3/test_roles.py
index 24c7b83..90dccca 100644
--- a/tempest/api/identity/admin/v3/test_roles.py
+++ b/tempest/api/identity/admin/v3/test_roles.py
@@ -73,7 +73,7 @@
         self.assertIn(role_id, fetched_role_ids)
 
     @test.attr(type='smoke')
-    def test_role_create_update_get(self):
+    def test_role_create_update_get_list(self):
         r_name = data_utils.rand_name('Role-')
         resp, role = self.client.create_role(r_name)
         self.addCleanup(self.client.delete_role, role['id'])
@@ -94,6 +94,10 @@
         self.assertEqual(new_name, new_role['name'])
         self.assertEqual(updated_role['id'], new_role['id'])
 
+        resp, roles = self.client.list_roles()
+        self.assertEqual(resp['status'], '200')
+        self.assertIn(role['id'], [r['id'] for r in roles])
+
     @test.attr(type='smoke')
     def test_grant_list_revoke_role_to_user_on_project(self):
         resp, _ = self.client.assign_user_role_on_project(
diff --git a/tempest/services/identity/v3/json/identity_client.py b/tempest/services/identity/v3/json/identity_client.py
index 35d8aa0..fdef83f 100644
--- a/tempest/services/identity/v3/json/identity_client.py
+++ b/tempest/services/identity/v3/json/identity_client.py
@@ -163,6 +163,12 @@
         body = json.loads(body)
         return resp, body['role']
 
+    def list_roles(self):
+        """Get the list of Roles."""
+        resp, body = self.get("roles")
+        body = json.loads(body)
+        return resp, body['roles']
+
     def update_role(self, name, role_id):
         """Create a Role."""
         post_body = {
diff --git a/tempest/services/identity/v3/xml/identity_client.py b/tempest/services/identity/v3/xml/identity_client.py
index 8f42924..7646df5 100644
--- a/tempest/services/identity/v3/xml/identity_client.py
+++ b/tempest/services/identity/v3/xml/identity_client.py
@@ -217,6 +217,12 @@
         body = self._parse_body(etree.fromstring(body))
         return resp, body
 
+    def list_roles(self):
+        """Get the list of Roles."""
+        resp, body = self.get("roles")
+        body = self._parse_roles(etree.fromstring(body))
+        return resp, body
+
     def update_role(self, name, role_id):
         """Updates a Role."""
         post_body = common.Element("role",