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
diff --git a/tempest/api/identity/admin/v3/test_tokens.py b/tempest/api/identity/admin/v3/test_tokens.py
index 22d74d3..f8a62a6 100644
--- a/tempest/api/identity/admin/v3/test_tokens.py
+++ b/tempest/api/identity/admin/v3/test_tokens.py
@@ -19,13 +19,11 @@
 from tempest.common.utils.data_utils import rand_name
 from tempest import exceptions
 from tempest.test import attr
-import testtools
 
 
 class UsersTestJSON(base.BaseIdentityAdminTest):
     _interface = 'json'
 
-    @testtools.skip("Skipped until the Bug #1221889 is resolved")
     @attr(type='smoke')
     def test_tokens(self):
         # Valid user's token is authenticated
@@ -51,7 +49,7 @@
         self.assertEqual(token_details['user']['name'], u_name)
         # Perform Delete Token
         resp, _ = self.v3_client.delete_token(subject_token)
-        self.assertRaises(exceptions.Unauthorized, self.v3_client.get_token,
+        self.assertRaises(exceptions.NotFound, self.v3_client.get_token,
                           subject_token)