Revise camera HAL 2, and add unit test skeleton.

Revise camera HAL 2, and add unit test skeleton.

- Add missing method in stream_ops (set_buffers_geometry)

- Remove extra method in stream_ops (set_swap_interval)

- Document metadata queue protocol

- Change metadata queue methods to be set/get through function calls
  only, instead of a struct member in the HAL device ops.

- Change vendor extension tag query methods to be retrieved by a get
  call, instead of a struct member in the HAL device ops.

- Add basic gtest unit test skeleton, which currently just returns
  static info from all camera devices.

Change-Id: I94117097b0243023ad60638070cc7f0cefec18e6