Python-2.6 compatibility for tests/test_keyring.py

TestCase.setUpClass() and unittest.SkipTest are features added in 2.7.
Calling super(KeyringTest, cls).setUpClass() could have never worked
since tests.utils.TestCase doesn't implement that (class) method.

Change-Id: Ifbb0465be24fd13ad68d52c0d7fa4c5090d0f694
Merge "Python-2.6 compatibility for tests/test_keyring.py"