allow multiple delayed_job processes

This allows specifying multiple delayed job instances per application,
and allows per application and per-worker customization.

{
  "deploy": {
    "my_app": {
      "delayed_job": [
        {
          "identifier": "regular",
          "timeout": 60
        },
        {
          "identifier": "priority",
          "options": "--min-priority 10",
          "timeout": 30
        }
      ]
    }
  }
}

Change-Id: I9699a500e6c231b37beabd951aaed2773a10b74d