CA-403620: Make the stunnel proxy local port configurable

Making it configurable can avoid the situation when the port conflicts
with others, e.g. an external program from users.

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

ocaml/xapi/xapi_globs.ml

@@ -1143,6 +1143,7 @@ let xapi_globs_spec =
   ; ("max_traces", Int max_traces)
   ; ("max_observer_file_size", Int max_observer_file_size)
   ; ("test-open", Int test_open) (* for consistency with xenopsd *)
+  ; ("local_yum_repo_port", Int local_yum_repo_port)
   ]
 
 let xapi_globs_spec_with_descriptions = []