libstagefright: Fix ANR issue in HTTP Streaming

The root cause of the ANRs during this usecase is the
blocking nature of the read calls on the network data
source due to which application thread gets blocked on
some lock in framework.

Fixes ANR during seek/pause during HTTP streaming
* Non-blocking read implmentation for NuCachedSource2
* Other framework related changes to handle underruns

Change-Id: Ief280b7e23727606746e1ca2bf4caa4a3044b7bc
Add 2 APIs (suspend/resume) in MediaPlayer

- API:suspend() will just pause the player and release all the decoders
  to replace release() which will release the whole player
- API:resume() will just init the decoders again,
  then start() will be called to start to play the streaming
- Add a check in AwesomePlayer::onVideoEvent()
  to make sure the first seek operation will always seek the next i-frame

Change-Id: Ie4c82906a2a056378119921a656128ebdc1007c4