httplive: Dont resume if we have almost fetched till stop time

- Use the last enqueued instead of last dequeued time in
  ResumeUntil.
- Set duration in access unit meta as timestamp difference
  between the last two queued access units.

CRs-Fixed: 759588

Change-Id: If53ddee1d87775905a6d4f11a6219fe66f498450