Comment 5 for bug 1260916

And I find this in test_shell.py:

# Test os-identity-api-version fall back to 2.0
shell('--os-identity-api-version 3.0 user-list')
assert do_tenant_mock.called
self.assertTrue(b.os_identity_api_version, '2.0')

This means the program is desiged to use 2.0.