title: Order of InsertManyResult.inserted_ids in case of unordered bulk insert
body: <p>I'm wondering if the order of ids of <code>InsertManyResult.inserted_ids</code> returned by an <strong>un-ordered</strong> bulk insert is consistent with the order of the input array? i.e that the first id from <code>InsertManyResult.inserted_ids</code> corresponds to the id of the first item of the input array</p>
  
  <p>In fact, if I consider the following example:</p>
  
  <pre class="lang-py prettyprint-override"><code>from pymongo import *
  
  connection = MongoClient()
  
  users = [{'name': 'John'}, {'name': 'Bob'}, {'name': 'Hulk'}]
  r = connection.testdb.user.insert_many(users, ordered=False)
  
  print(r.inserted_ids)
  print(users)
  </code></pre>
  
  <p>which prints the following:</p>
  
  <pre><code>[ObjectId('5d8bc14424c4cb24ac1d2334'),
   ObjectId('5d8bc14424c4cb24ac1d2335'),
   ObjectId('5d8bc14424c4cb24ac1d2336')]
  
  [{'_id': ObjectId('5d8bc14424c4cb24ac1d2334'), 'name': 'John'},
   {'_id': ObjectId('5d8bc14424c4cb24ac1d2335'), 'name': 'Bob'},
   {'_id': ObjectId('5d8bc14424c4cb24ac1d2336'), 'name': 'Hulk'}]
  </code></pre>
  
  <p>In this simple example, the order is respected but due to the un-ordered nature of the insert, I'm wondering if it is always guaranteed</p>