api-ref: body verification for abort live migration

This completes the DELETE method body verification
for server migrations.

This was only supported in microversion >= 2.24 and only
on the libvirt driver so there are notes about it being
conditional.

Closes-Bug: #1641713

Part of blueprint api-ref-in-rst-ocata

Change-Id: I3bc2cb70f8ad12124098376ef01eb7df2f6b2f88

api-ref/source/server-migrations.inc

@@ -1,5 +1,4 @@
 .. -*- rst -*-
-.. needs:body_verification
 
 =========================================
  Server migrations (servers, migrations)
@@ -179,6 +178,45 @@ Delete (Abort) Migration
 
 .. rest_method:: DELETE /servers/{server_id}/migrations/{migration_id}
 
+Abort an in-progress live migration.
+
+.. note:: Microversion 2.24 or greater is required for this API.
+
+.. note:: Not all compute back ends support aborting an in-progress live
+    migration.
+
+Policy defaults enable only users with the administrative role to perform
+this operation. Cloud providers can change these permissions through the
+``policy.json`` file.
+
+**Preconditions**
+
+The server OS-EXT-STS:task_state value must be ``migrating``.
+
+If the server is locked, you must have administrator privileges to force the
+completion of the server migration.
+
+The migration status must be ``running``.
+
+**Asynchronous Postconditions**
+
+After you make this request, you typically must keep polling the server status
+to determine whether the request succeeded. You may also monitor the migration
+using::
+
+    GET /servers/{server_id}/migrations/{migration_id}
+
+**Troubleshooting**
+
+If the server task_state remains ``migrating`` for an inordinate amount of
+time, the request may have failed. Ensure you meet the preconditions and run
+the request again. If the request fails again, investigate the compute back
+end.
+
+Normal response codes: 202
+
+Error response codes: badRequest(400), unauthorized(401), forbidden(403), itemNotFound(404), conflict(409)
+
 Request
 -------