AddDirectory false if we are running DQ monitoring
Set a ROOT global flag to False - prevents histograms from being assigned to a TDirectory by default, an action that is thread-unsafe and causes subtle bugs in MT. (e.g. ATLASRECTS-6029 probably.)
I've done this in the base class of the new-style monitoring which I don't think is really optimal, since it definitely will cause other code to see different ROOT environments depending on whether monitoring is on or off, but perhaps someone can make a better suggestion.