Add LFN in exception context in Root{Primary,Secondary}FileSequence constructor

[makortel]

Motivated by the exception messages shown in cms-sw/cmssw#44878 that show file read errors while constructing PoolSource without information on what file was being read. The try-catch could be placed elsewhere though (Root{Primary,Secondary}FileSequence being our best guess now.

[makortel]

Or perhaps all root file accesses in RootFile class would need try-catch that adds the file name in the exception message.