title: Can't create backup mongodump with --db. Authentication failed
body: <p>When I create backup of all databases in MongoDB (version 3):</p>
  
  <pre><code>mongodump --username bacUser --password 12345
  </code></pre>
  
  <p>It's OK. But when I try to create backup of a selected db:</p>
  
  <pre><code>mongodump --username bacUser --password 12345 --db test
  </code></pre>
  
  <p>It gives me this error:</p>
  
  <blockquote>
    <p>Failed: error connecting to db server: server returned error on SASL authentication step: Authentication failed.</p>
  </blockquote>