Phedex node name returned by listFileBlockLocation

first iteration, fixes #5167

@ticoann I have made the pull request now as it may be easier to have a conversation with the changes available. Also I recall you said it's easier for you to track as a pull request.

Cheers
Alex
https://cmsweb.cern.ch/phedex/datasvc/doc/blockreplicas
I think that key exists, but we should make sure by testing later.