Add filter for disabled users to superuser user list API

Fixes https://jira.coreos.com/browse/QS-102

endpoints/api/test/test_superuser.py

@@ -0,0 +1,19 @@
+import pytest
+
+from endpoints.api.superuser import SuperUserList
+from endpoints.api.test.shared import conduct_api_call
+from endpoints.test.shared import client_with_identity
+from test.fixtures import *
+
+@pytest.mark.parametrize('disabled', [
+  (True),
+  (False),
+])
+def test_list_all_users(disabled, client):
+  with client_with_identity('devtable', client) as cl:
+    params = {'disabled': disabled}
+    result = conduct_api_call(cl, SuperUserList, 'GET', params, None, 200).json
+    assert len(result['users'])
+    for user in result['users']:
+      if not disabled:
+        assert user['enabled']