If enabled, allow users and orgs to set their time machine expiration

Fixes https://www.pivotaltracker.com/story/show/142881203

endpoints/api/test/test_organization.py

@@ -0,0 +1,18 @@
+import pytest
+
+from data import model
+from endpoints.api import api
+from endpoints.api.test.shared import client_with_identity, conduct_api_call
+from endpoints.api.organization import Organization
+from test.fixtures import app, appconfig, database_uri, init_db_path, sqlitedb_file
+
+@pytest.mark.parametrize('expiration, expected_code', [
+    (0, 200),
+    (100, 400),
+    (100000000000000000000, 400),
+])
+def test_change_tag_expiration(expiration, expected_code, client):
+  with client_with_identity('devtable', client) as cl:
+    conduct_api_call(cl, Organization, 'PUT', {'orgname': 'buynlarge'},
+                     body={'tag_expiration_s': expiration},
+                     expected_code=expected_code)