Add more answer_dist coverage.

Also resolve remaining PEP8 warnings.

Change-Id: I1e5e1947ededbba97540e661c3fb6adcac100597

edx/analytics/tasks/reports/tests/test_incremental_enrollments.py

@@ -277,8 +277,6 @@ class TestWeeklyIncrementalUsersAndEnrollments(unittest.TestCase):
         self.assertEqual(res.loc[self.row_label('enrollment_change')]['2013-01-15'], 2)
 
 
-
-
 class TestDailyRegistrationsEnrollmentsAndCourses(unittest.TestCase):
     """Tests for DailyRegistrationsEnrollmentsAndCourses class."""