Add credit enrollment mode

analyticsclient/constants/enrollment_modes.py

 AUDIT = u'audit'
+CREDIT = u'credit'
 HONOR = u'honor'
 PROFESSIONAL = u'professional'
 VERIFIED = u'verified'
 
-ALL = [AUDIT, HONOR, PROFESSIONAL, VERIFIED]
+ALL = [AUDIT, CREDIT, HONOR, PROFESSIONAL, VERIFIED]

analyticsclient/tests/test_helpers.py

@@ -37,6 +37,7 @@ class HelperTests(TestCase):
 
     def test_enrollment_modes(self):
         self.assertEqual('audit', enrollment_modes.AUDIT)
+        self.assertEqual('credit', enrollment_modes.CREDIT)
         self.assertEqual('honor', enrollment_modes.HONOR)
         self.assertEqual('professional', enrollment_modes.PROFESSIONAL)
         self.assertEqual('verified', enrollment_modes.VERIFIED)