coverity fixes

After the latest installation of coverity (Q4/2018) with > c++11 support we can re-run coverity. This merge request proposes various fixes throughout the project following issues found by coverity. To find the individual issue pls check the "Gaudi" project on the coverity.cern.ch server (owner 'roiser'). NB: There are another ~ 50 Gaudi (mostly medium/minor) issues which have not been addressed yet.