Fix build against current Nix master

Dependencies

• [2] BYVRA54Q Temporarily disable machines on any exception, not just connection failures
• [3] BG6PEOB2 Make the output size limit configurable
• [*] 5AIYUMTB Basic remote building

Change contents

• edit in src/hydra-queue-runner/build-remote.cc at line 288
  [2.5695]→[2.5695:5945](∅→∅)
  − case BuildResult::CachedFailure: // cached on the build machine

  − result.stepStatus = bsCachedFailure;

  − result.canCache = true;

  − result.errorMsg = "";

  − break;