improvements to CRAB recovery

[belforte]

Possible enhancementa/improvements, see also https://cms-talk.web.cern.ch/t/how-to-force-resubmitting-specific-jobs-when-they-appear-as-completed-in-crab/133621

• improve help: strategy is not clearly documented
• make it possible to re-run completed jobs, in case users delete/loose some files
  • i.e. add jobids strategy
• instructions for how to find the recovery config so that users can change e.g. splitting
• a dry run mode to make it easy and painless to do the previous
• a clone mode ?