Fix log file messages when using Histograming::Sink::Base

Changed the messages output by Histograming::Sink::Base and RootHistCnv::PersSvc, so if the default output file for RootHistCnv::PersSvc is still set it does not print anything, also add a log file message to Histograming::Sink::Base for the file name to be used and again after each stop when the histograms are written.