Simplify test_only_expected_fields_are_displayed

Use sets to accomplish the same result.

common/test/acceptance/tests/studio/test_studio_settings.py

@@ -397,10 +397,17 @@ class AdvancedSettingsValidationTest(StudioCourseTest):
         When I view the Advanced Settings screen for the course
         The total number of fields displayed matches the number I expect
         And the actual fields displayed match the fields I expect to see
+
+        Note that this test will NOT fail if fields that we expect to see are
+        not displayed, only if fields show up that we did not expect to see.
         """
         expected_fields = self.advanced_settings.expected_settings_names
         displayed_fields = self.advanced_settings.displayed_settings_names
-        self.assertEqual(len(expected_fields), len(displayed_fields))
-        for field in displayed_fields:
-            if field not in expected_fields:
-                self.fail("Field '{}' not expected for Advanced Settings display.".format(field))
+        unexpectedly_displayed = set(displayed_fields) - set(expected_fields)
+        self.assertEquals(
+            len(unexpectedly_displayed),
+            0,
+            "The following fields were unexpectedly displayed: {fields}".format(
+                fields=", ".join(unexpectedly_displayed)
+            )
+        )