title: Gerrit: remote rejected (you are not allowed to upload merges) even though I allowed "Push merge commit"
body: <p>I've configured Gerrit to allow <code>Push Merge Commit</code> on my branch, but I still get the following error when I try to push a merge commit:</p>
  
  <pre><code>! [remote rejected] ANDROID-foo -&gt; ANDROID-foo (you are not allowed to upload merges)
  </code></pre>
  
  <p>I'm running Gerrit 2.8-1-gaa9367b.</p>