title: expireAfterSeconds doesnt work mongo
body: <p>Using Mongo 3.2</p>
  
  <p>I set expireAfterSeconds to 3 days, because we do not need more then 3 days of data on this collection, but I can see in the db, that we still have data from a month ago. Is something configured wrong.</p>
  
  <p>The info gather from db.runs.getIndexes()</p>
  
  <pre class="lang-js prettyprint-override"><code>{
     "v" : 1,
     "key" : {
        "_id" : 1
      },
     "name" : "_id_",
     "ns" : "guardian.runs"
  },
  {
     "v" : 1,
     "key" : {
       "created" : 1
     },
     "name" : "created_1",
     "ns" : "guardian.runs",
     "background" : true,
     "expireAfterSeconds" : 259200
  }
  </code></pre>
  
  <p>An entry that should be deleted:</p>
  
  <pre class="lang-js prettyprint-override"><code> [
     {
       "_id": "578c8aa25a3f72387073f2f0",
       "job_id": "573f62bf0e44a2796b6e9de1",
       "owner": null,
       "started": "2016-07-18T07:52:02.447Z",
       "ended": "2016-07-18T07:52:14.119Z",
       "status": "success",
       "result": {
         "success": [],
         "fail": [],
         "warning": []
       }
     }
  ]
  </code></pre>