CA-389319: Wait and retry for GET_UPDATES_IN_PROGRESS

The query on HTTP endpoint /updates will return the available updates in
JSON format. Prior to the changes in this commit, if a query arrives
when another query is being handled, a "GET_UPDATES_IN_PROGRESS" error
will be returned immediately. This behaviour is not friendly to GUI
client XenCenter.

In this commit, the behaviour is changed to wait and retry in handling
the query in xapi since the "*_IN_PROGGRESS" error is a transient
failure. Tolerating it in xapi (server) side avoids error handling in
client side.

Signed-off-by: Ming Lu <ming.lu@cloud.com>

Author: minglumlu

ocaml/xapi/helpers.ml

@@ -1654,8 +1654,9 @@ let retry ~__context ~doc ?(policy = Policy.standard) f =
       ) ;
       f ()
     with
-    | Api_errors.Server_error (code, _ :: _) as e
+    | Api_errors.Server_error (code, _) as e
     when code = Api_errors.other_operation_in_progress
+         || code = Api_errors.get_updates_in_progress
     ->
       debug "%s locking failed: caught transient failure %s" doc
         (ExnHelper.string_of_exn e) ;