Attempt to fix lhe-only production

Hi @ewelina,

This is an attempt to fix lhe-file-only production, both in the old and the new workflow. The problem with what we have currently is that if the user specifies e.g. --outputTXTFile=TXT.tar.gz, then Powheg (for example) produces a lhe file with the name TXT.events, creates its tarball TXT.tar.gz, but then the transform would create a symlink from TXT.events into TXT.tar.gz - that is, the tarball is erased. I think this is the reason why I couldn't do it properly on the grid (for bb4l, but this is true for anything a priori). If the user provides both a --outputTXTFile and a --outputEVNTFile, the behaviour is correct.

So what I did is to come back with events.lhe for the symlink. I tested everything locally and it looks ok.