Test tweaks for more API coverage

- Allow for customizable result classes (i.e. Config Mixin can define
  these)
- Section out streaming and non-streaming views tests
- Use TranscoderPP instead of Transcoder (FFI doesn't play well with
  'Transcoder')
- Unskip some tests which were previously skipped under PyPy

Change-Id: Ia43c9adc3caa08947cafcb1f9b82c898b3787ede
Reviewed-on: http://review.couchbase.org/29779
Reviewed-by: Mark Nunberg <mnunberg@haskalah.org>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>