title: RxJava: Merge multiple singles and complete after some have failed
body: <p>I would like to merge two <code>Single&lt;MyData&gt;</code> such that if one of them fails but the other one succeeds then the error of the one that failed and the emission from the other one are reported, and then the resulting <code>Single&lt;MyData&gt;</code> (or <code>Observable&lt;MyData&gt;</code>) completes.</p>
  
  <p>If both <code>Single&lt;MyData&gt;</code> fail then the result should also fail and also be marked as failed.</p>
  
  <p>What I would like to have at the end is:</p>
  
  <ul>
  <li>If both succeed then the emitted values and a producer marked as completed. </li>
  <li>If one succeeds and the other fails, the emitted value, the thrown error and the producer marked as complete.</li>
  <li>If all fail, the errors and the producer marked as failed.</li>
  </ul>
  
  <p>It's like an 'OR' operation</p>