DPL Analysis: workaround to publish histograms also with pipelining

For some reason if the histograms arrive all at once, they get dropped.
Not yet sure why that happens. It clearly cannot merely be a matter of
"older possible timeframe" being wrong, nor a problem with the order of
the end of stream, because otherwise I would expect also this to fail.

Framework/Core/include/Framework/AnalysisManagers.h

@@ -287,6 +287,7 @@ struct OutputManager<HistogramRegistry> {
     auto& deviceSpec = context.services().get<o2::framework::DeviceSpec const>();
     context.outputs().snapshot(what.ref(deviceSpec.inputTimesliceId, deviceSpec.maxInputTimeslices), *(what.getListOfHistograms()));
     what.clean();
+    sleep(deviceSpec.inputTimesliceId);
     return true;
   }
 };
@@ -314,6 +315,7 @@ struct OutputManager<OutputObj<T>> {
   {
     auto& deviceSpec = context.services().get<o2::framework::DeviceSpec const>();
     context.outputs().snapshot(what.ref(deviceSpec.inputTimesliceId, deviceSpec.maxInputTimeslices), *what);
+    sleep(deviceSpec.inputTimesliceId);
     return true;
   }
 };