Fix test keystone.tests.unit.test_token_bind.BindTest
Fix test keystone.tests.unit.test_token_bind.BindTest

[token] enforce_token_bind option was deprecated for removal, and
the 'bind' option doesn't enforce a set of choices. I think the better
option here would be to remove the choices field and let the backend
enforce correctness.

Partial-Bug: #1686921
Change-Id: If0a537237a477303c0ce84945d83ce440f4d7812

rajalokan/keystone,rajalokan/keystone,openstack/keystone,mahak/keystone,openstack/keystone,mahak/keystone,openstack/keystone,mahak/keystone,rajalokan/keystone