Correct policy action for check_endpoint_group test

Currently ``check_endpoint_group`` test is testing the wrong
policy action causing the test to be skipped in the gates [0].
This commit corrects the policy action to what is actually
enforced in the code [1].

[0] http://logs.openstack.org/10/483110/1/check/gate-tempest-dsvm-patrole-member-ubuntu-xenial/f821202/console.html#_2017-07-12_22_43_39_986182
[1] https://github.com/openstack/keystone/blob/a43d5a6893a5753f8567206032e779930ddd4321/keystone/common/policies/endpoint_group.py#L37

Change-Id: I0cb7c513513674de3bddb7595899607780ae45b6
1 file changed