When checking if build is already built, check for potential 'failed with result'. Fixes issue #7.

Dependencies

• [2] RXVJFQ5A Evaluator cleanups
• [3] 3XTHEUMP * Implemented the clone feature.
• [*] OOQ2D3KC * Refactoring: move fetchInput out of hydra_scheduler into a separate

Change contents

• replacement in src/lib/Hydra/Helper/AddBuilds.pm at line 890
  [2.1038]→[2.1038:1073](∅→∅)
  − , buildstatus => 0
  [2.1038]

  [2.1073]
  + , buildstatus => -f "$outPath/nix-support/failed" ? 6 : 0