refactoring to get master function, instead of passing master values directly

this will enable retrying later

weed/server/master_server_handlers_admin.go

@@ -125,13 +125,13 @@ func (ms *MasterServer) selfUrl(r *http.Request) string {
 }
 func (ms *MasterServer) submitFromMasterServerHandler(w http.ResponseWriter, r *http.Request) {
 	if ms.Topo.IsLeader() {
-		submitForClientHandler(w, r, ms.selfUrl(r), ms.grpcDialOption)
+		submitForClientHandler(w, r, func()string{return ms.selfUrl(r)}, ms.grpcDialOption)
 	} else {
 		masterUrl, err := ms.Topo.Leader()
 		if err != nil {
 			writeJsonError(w, r, http.StatusInternalServerError, err)
 		} else {
-			submitForClientHandler(w, r, masterUrl, ms.grpcDialOption)
+			submitForClientHandler(w, r, func()string{return masterUrl}, ms.grpcDialOption)
 		}
 	}
 }