Wake the dispatcher when the machines file has changed

Dependencies

• [2] SODOV2CM Automatically reload $NIX_REMOTE_SYSTEMS when it changes
• [*] 24BMQDZA Start of single-process hydra-queue-runner
• [*] 5AIYUMTB Basic remote building

Change contents

• edit in src/hydra-queue-runner/hydra-queue-runner.cc at line 99
  [5.9439]

  [2.3290]
  +

  + wakeDispatcher();