title: How to discard changes using repo
body: <p><code>repo status</code> shows me a lot of un-wanted changes. </p>
  
  <p>It would be duplicated if I enter every project and use <code>git reset --hard</code>. </p>
  
  <p>Is there a way to reset all the changes using repo, something like <code>repo reset --hard</code>?</p>