hiracchi/docker-ffmpeg

ffmpeg using hwaccels

* building test for ffmpeg on ubuntu

* references
  - https://trac.ffmpeg.org/wiki/CompilationGuide/Ubuntu
  - https://qiita.com/tappie/items/6ca070f4e9d461961eda

* confirm
  - `vainfo`
  - `ffmpeg -hwaccels`
  - `ffmpeg -encoders 2>/dev/null |fgrep vaapi`