Fix TTS for Zen mode voice activity.

Don't finish activity until TTS has finished.
Incorrect TTS for mix of hours / mins - e.g. 1 hour 45 minutes.
Improve the description of TTS strings for translators.

BUG: 20248251
BUG: 21413212
BUG: 21411622

Change-Id: Id2693ea82b76492216147012216ba07ce75a9d12