title: How to check if SCNAction has completed in Swift 3
body: <p>Here i have a group of animations that act on a <code>SCNSphere</code> called <code>testNode</code></p>
  
  <pre><code>//run this during the duration of the two animations below
  earthNode.runAction(SCNAction.rotateBy(x: 0, y: 5, z: 5, duration: 4))
  //run this action right away
  earthNode.runAction(SCNAction.moveBy(x: 0, y: 0, z: -5, duration: 2))
  //RUN THIS ACTION AFTER ACTION ABOVE IS COMPLETED
  earthNode.runAction(SCNAction.moveBy(x: 0, y: 0, z: 5, duration: 2))
  </code></pre>
  
  <p>I am trying to stop the last two animations from happening at the same time. How can i check if the second animation is completed to then run the last animation listed. I would also appreciate an explanation to checking if a group of animations running at the same time are finished.</p>