248e401 backend: expect removed directories while trying to list them

Authored and Committed by frostyx 4 years ago
    backend: expect removed directories while trying to list them
    
    While recursively walking through the results directory, expect
    that some of the directories may be deleted in the meantime.
    
    With this change, I was able to successfully finish a run of the
    `copr_print_results_to_delete.py` script on the production instance.