348f544 avoid scary noise from TaskStdoutProtocol

Authored and Committed by Dan Callaghan 6 years ago
    avoid scary noise from TaskStdoutProtocol
    
    We can continue logging the detailed traces at DEBUG level only, which
    will normally not be shown. We only want to know about it if a process
    exits non-zero, since that means something went wrong in
    rhts-test-runner.
    
    Change-Id: Ie960c6db9e7f5bc79c0a9e80270054166bdf7d50