xml2json recursively search for the root data file

[kratsg]

Description

When running xml2json, it's often configured that the input file prefix is results/<analysis name>/<filename>.root which is not necessarily something I make initially when I copy over the files. In these cases, I'd want xml2json to just search the directory I'm running in for the root file (i.e. using its basename).

[lukasheinrich]

this would break compatibility with hist2workspace no? I'd rather see the ROOT-aware scripts handling this (beyond just dumping PrintXML())

[kratsg]

Well, I'd just want xml2json to be a bit more flexible -- but this won't break the hist2workspace compatibility (it's only in the import direction to be flexible).