G4AtlasTests: Fix use of detector store.
ZDCHitsTestTool was accessing the detector store in the constructor. But this is run also during genconf, so this (at best) will generate bogus warnings. Move this to initialize().
ZDCHitsTestTool was accessing the detector store in the constructor. But this is run also during genconf, so this (at best) will generate bogus warnings. Move this to initialize().