Build Script Cleanup, master branch (2019.10.18.)

Updated the build scripts to use the -x arguments more consistently. As we found in ATLINFR-3221, unfortunately there were a lot of inconsistencies with this command line argument. 😦

Note that I did not update every single script.

• AthDataQuality/build_externals.sh doesn't actually build anything, it only checks out some code. So a -x argument would be meaningless for this script.
• I didn't touch the AnalysisTop files, as hopefully that project will not exist by the time that we get to Run-3, so I don't want to spend any effort on it in this branch.

At the same time made some unrelated fixes/cleanups as well. Note however that the scripts are not all consistent even after this update. Much of this is just a personal dislike for some of the formalism used in the Athena project. So I don't want to copy that formalism to the other projects. 😦 At the same time I also don't want to change the code in Athena, which Oleg worked on quite a bit a while ago.

As stated in ATLINFR-3221, we need this update before we could start the Python 3 nightlies...