title: Check if Jenkins node is online for the job, otherwise send email alert
body: <p>Having the Jenkins job dedicated to special node I'd like to have a notification if the job can't be run because the node is offline. Is it possible to set up this functionality?</p>
  
  <p>In other words, the default Jenkins behavior is waiting for the node if the job has been started when the node is offline ('pending' job status). I want to fail (or don't start at all) the job in this case and send 'node offline' mail.</p>
  
  <p>This node checking stuff should be inside the job because the job is executed rarely and I don't care if the node is offline when it's not needed for the job. I've tried external node watching plugin, but it doesn't do exactly what I want - it triggers emails every time the node goes offline and it's redundant in my case.</p>