Fixed payment page bug

Using SKU to choose course mode when creating an order.

ECOM-2172

common/djangoapps/course_modes/models.py

@@ -126,6 +126,16 @@ class CourseMode(models.Model):
         self.currency = self.currency.lower()
         super(CourseMode, self).save(force_insert, force_update, using)
 
+    @property
+    def slug(self):
+        """
+        Returns mode_slug
+
+        NOTE (CCB): This is a silly hack needed because all of the class methods use tuples
+        with a property named slug instead of mode_slug.
+        """
+        return self.mode_slug
+
     @classmethod
     def all_modes_for_courses(cls, course_id_list):
         """Find all modes for a list of course IDs, including expired modes.