Unskip test_tokens and update expected status to 404 from 401

Now that the API results in a 404 for an invalid x-subject-token
and a 401 for an invalid x-auth-token, we need to update the expected
resulting HTTP Status from 401 to 404 in the test_tokens test.

closes-bug: 1221889
Change-Id: I158c968c1948ee658305e9ec484425d98f187cba
Merge "Unskip test_tokens and update expected status to 404 from 401"