Adds keystone roles v2 tests in v3

This submission is to add the tests missing in v3 and present in v2.
Submitting roles test cases.

Change-Id: I0e995848ed0019a4895cdff2b70795b5eaf9795a
diff --git a/tempest/api/identity/admin/v3/test_roles.py b/tempest/api/identity/admin/v3/test_roles.py
index 90dccca..b680b64 100644
--- a/tempest/api/identity/admin/v3/test_roles.py
+++ b/tempest/api/identity/admin/v3/test_roles.py
@@ -25,6 +25,10 @@
     @test.safe_setup
     def setUpClass(cls):
         super(RolesV3TestJSON, cls).setUpClass()
+        for _ in range(3):
+            role_name = data_utils.rand_name(name='role-')
+            _, role = cls.client.create_role(role_name)
+            cls.data.v3_roles.append(role)
         cls.fetched_role_ids = list()
         u_name = data_utils.rand_name('user-')
         u_desc = '%s description' % u_name
@@ -186,6 +190,14 @@
             self.domain['id'], self.group_body['id'], self.role['id'])
         self.assertEqual(resp['status'], '204')
 
+    @test.attr(type='gate')
+    def test_list_roles(self):
+        # Return a list of all roles
+        resp, body = self.client.list_roles()
+        self.assertEqual(200, resp.status)
+        found = [role for role in body if role in self.data.v3_roles]
+        self.assertEqual(len(found), len(self.data.v3_roles))
+
 
 class RolesV3TestXML(RolesV3TestJSON):
     _interface = 'xml'