Fix test for new WebOb

In the change from WebOb 1.5.1 to 1.6.0, WebOb no longer adds a charset
when the content-type is application/json.

http://docs.webob.org/en/stable/whatsnew-1.6.html#bugfixes

Change-Id: I78431f295e891ddaf38809d7de55a7195fb9432d
diff --git a/tests/test_scheduler.py b/tests/test_scheduler.py
index 499786c..b585fea 100755
--- a/tests/test_scheduler.py
+++ b/tests/test_scheduler.py
@@ -2242,8 +2242,8 @@
         headers = f.info()
         self.assertIn('Content-Length', headers)
         self.assertIn('Content-Type', headers)
-        self.assertEqual(headers['Content-Type'],
-                         'application/json; charset=UTF-8')
+        self.assertIsNotNone(re.match('^application/json(; charset=UTF-8)?$',
+                                      headers['Content-Type']))
         self.assertIn('Access-Control-Allow-Origin', headers)
         self.assertIn('Cache-Control', headers)
         self.assertIn('Last-Modified', headers)