Add delete_on_termination for compute API v2.79 - os-volume_attachments

This adds delete_on_termination field for the compute API response schema
for the 2.79 microversion in the following APIs:

  - GET /servers/{server_id}/os-volume_attachments (list)
  - GET /servers/{server_id}/os-volume_attachments/{volume_id} (show)
  - POST /servers/{server_id}/os-volume_attachments (attach)

Change-Id: I7a9b22477b800c6d60acb67c27aff5dcb61d7875
diff --git a/doc/source/microversion_testing.rst b/doc/source/microversion_testing.rst
index 06062c2..f37342e 100644
--- a/doc/source/microversion_testing.rst
+++ b/doc/source/microversion_testing.rst
@@ -426,6 +426,10 @@
 
   .. _2.73: https://docs.openstack.org/nova/latest/reference/api-microversion-history.html#id66
 
+  * `2.79`_
+
+  .. _2.79: https://docs.openstack.org/nova/latest/reference/api-microversion-history.html#maximum-in-train 
+
 * Volume
 
   * `3.3`_