make is_masquerading_as_student work with Mock for tests

lms/djangoapps/courseware/masquerade.py

@@ -58,4 +58,4 @@ def is_masquerading_as_student(user):
     Return True if user is masquerading as a student, False otherwise
     '''
     masq = getattr(user, 'masquerade_as_student', False)
-    return masq
+    return masq==True