Add some debug code

Dependencies

• [2] 46ADBTMQ Start steps in order of ascending build ID
• [3] 4I2HF4L3 Unindent
• [4] PDJCVDVY Fix segfault sorting runnable steps
• [5] TTBLPQAJ Keep track of wait time per system type
• [6] 5N7LVAJN Keep track of requiredSystemFeatures in the machine stats
• [7] EYR3EW6J Keep stats for the Hydra auto scaler
• [*] MHVIT4JY Split hydra-queue-runner.cc more

Change contents

• replacement in src/hydra-queue-runner/dispatcher.cc at line 249
  [2.1281]→[2.1281:1344](∅→∅)
  − if (!mi.machine->supportsStep(step)) continue;
  [2.1281]

  [2.1344]
  + if (!mi.machine->supportsStep(step)) {

  + debug("machine '%s' does not support step '%s' (system type '%s')",

  + mi.machine->sshName, step->drvPath, step->drv.platform);

  + continue;

  + }