add playback THD / spectrum tests

- add spectrum test for playback : pass level may still require further tuning
- separate all_recording from all_playback
- add playback THD
- added download command to allow data generated from python
- change recording THD test to repeat only twice
- fix sound output in device side to be dependent on source

Change-Id: Ifb78a127a23e741bf29c520bb8e92ad6286f6426