Stop octopus animation when paused

Bug: 65597560
Test: 1. launch easter egg
         adb shell am start \
           -a android.intent.action.MAIN \
           -c com.android.internal.category.PLATLOGO
      2. go home
         adb shell input keyevent 3
      3. ensure octo is not consuming CPU
         adb shell top

Change-Id: I5e95e56ddb212f951b461264d3af40682d08fee3