Mute sound when phone is muted

This WILL cause tests to fail.

I tried to get it to work with Mockito, but the failing mock code below didn't do it.

Mockito.when(Mockito.mock(AudioManager.class).getRingerMode())
.thenReturn(AudioManager.RINGER_MODE_NORMAL);

Interstitials are annoying enough even without the phone screaming music even when you have muted the phone. This mutes the sound when the phone is in silent/vibrate mode.