frameworks/base/NuPlayer: Handle Seek from NuPlayer

- Seek was handled by the source by queuing discontinuity events
  individually for each stream.With this approach renderer will
  continue till discontinuity events are handled for each stream
- With the new approach seek is handled by the player -
  - get the new seek time from source
  - flush the source TS segments in LiveDataSource, access units
    in TS Parser, decoders and renderer
  - notify current position to driver
  - LiveSession will not queue a discontinuity for seek.
- Add a mutex lock for connect & disconnect ChromiumHTTPDataSource
- Handle flush in ACodec - Idle to Executing & Loaded to Idle states

Conflicts:

	media/libmediaplayerservice/nuplayer/NuPlayer.cpp

Change-Id: I8a741c2c665d3aca715734fc1fd1eeae33a6271b