title: Gerrit - cannot find user by email when using set-reviewers
body: <p>I've been trying to add users as reviewers to changes. I've stumbled upon a strange issue. If I identify users by their username, everything goes smoothly. If I identify them by email, Gerrit complains.</p>
  
  <p>what works:</p>
  
  <pre><code>ssh -p 29418 user@review.example.com gerrit set-reviewers --add username changeid
  </code></pre>
  
  <p>what doesn't work:</p>
  
  <pre><code>ssh -p 29418 user@review.example.com gerrit set-reviewers --add username@example.com changeid
  </code></pre>
  
  <p>The user has <em>username</em> as their user name and <em>username@example.com</em> as their email address.
  What Gerrit responds with is:</p>
  
  <pre><code>error: could not add username@example com: username@example.com does not identify a registered user or group
  </code></pre>