Draft: fixing some sychronization problems for accessors needed for multithreading of...

Starting from the Jira ATLASG-2957 ticket, I have localized the missing ReadHandleKey use for a ptvarcone decorator access. Rerunning I found two other problems which I fixed. The tests now are failing on access to HLT_IDTrack_Bjet_IDTrig.btagIp_trackDisplacement from Jet deco algs, which I haven't found where to put the read handle key. But these fixes would be useful for the debugging of the derivation multithreading. @ssnyder might check that my changes are ok...