Updated Commerce API to return CourseMode expiration date

XCOM-477

lms/djangoapps/commerce/api/v1/serializers.py

@@ -9,6 +9,7 @@ class CourseModeSerializer(serializers.ModelSerializer):
     """ CourseMode serializer. """
     name = serializers.CharField(source='mode_slug')
     price = serializers.IntegerField(source='min_price')
+    expires = serializers.DateTimeField(source='expiration_datetime', required=False, blank=True)
 
     def get_identity(self, data):
         try:
@@ -18,7 +19,7 @@ class CourseModeSerializer(serializers.ModelSerializer):
 
     class Meta(object):  # pylint: disable=missing-docstring
         model = CourseMode
-        fields = ('name', 'currency', 'price', 'sku')
+        fields = ('name', 'currency', 'price', 'sku', 'expires')
 
 
 class CourseSerializer(serializers.Serializer):

lms/djangoapps/commerce/api/v1/tests/test_views.py

@@ -35,7 +35,8 @@ class CourseApiViewTestMixin(object):
             u'name': course_mode.mode_slug,
             u'currency': course_mode.currency.lower(),
             u'price': course_mode.min_price,
-            u'sku': course_mode.sku
+            u'sku': course_mode.sku,
+            u'expires': course_mode.expiration_datetime,
         }