Fix a few issues we run into when running the discussion tests.

lms/djangoapps/course_goals/handlers.py

@@ -6,6 +6,7 @@ from __future__ import absolute_import
 from django.db import models
 from django.dispatch import receiver
 
+import six
 from course_modes.models import CourseMode
 from student.models import CourseEnrollment
 
@@ -20,7 +21,7 @@ def update_course_goal_on_enroll_change(sender, instance, **kwargs):  # pylint:
     1) Set the course goal to 'certify' when the user enrolls as a verified user.
     2) Remove the course goal when the user's enrollment is no longer active.
     """
-    course_id = str(instance.course_id).decode('utf8', 'ignore')
+    course_id = six.text_type(instance.course_id)
     if not instance.is_active:
         remove_course_goal(instance.user, course_id)
     elif instance.mode == CourseMode.VERIFIED:

openedx/core/lib/course_tabs.py

@@ -4,6 +4,8 @@ Tabs for courseware.
 from __future__ import absolute_import
 from openedx.core.lib.plugins import PluginManager
 
+from functools import cmp_to_key
+
 # Stevedore extension point namespaces
 COURSE_TAB_NAMESPACE = 'openedx.course_tab'
 
@@ -41,5 +43,5 @@ class CourseTabPluginManager(PluginManager):
             else:
                 return 1
         tab_types = list(cls.get_available_plugins().values())
-        tab_types.sort(cmp=compare_tabs)
+        tab_types.sort(key=cmp_to_key(compare_tabs))
         return tab_types