Improvements and clarifications for using XRootD

[knoepfel]

This issue has been migrated from https://cdcvs.fnal.gov/redmine/issues/23741 (FNAL account required) Originally created by @knoepfel on 2019-12-09 21:49:57

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This is a parent issue for all XRootD-related reports, insofar as they are related to art_root_io's use of ROOT's file-opening behavior.

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Subtasks:

• https://github.com/art-framework-suite/art-root-io/issues/2
• https://github.com/art-framework-suite/art-root-io/issues/3
• https://github.com/art-framework-suite/art-root-io/issues/4
• https://github.com/art-framework-suite/art-root-io/issues/6

[knoepfel]

Comment by @knoepfel on 2019-12-09 21:58:42

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due to changes in a related task: #23742