Docker image for arduino-esp8266 CI builds

Contains Arduino IDE, Python, git, and a copy of ESP8266 toolchain.

Usage

1. Build the image

   docker build -t arduino-docker .

2. Run the image

   cd arduino-esp866-dir
   docker run --rm -v $PWD:/build -it arduino-docker

3. Build arduino-esp8266 tests

   # install tools, can be done once
   cd tools
   cp /opt/dist/* dist/
   ./get.py
   cd ../
   
   # build tests
   cd tests/device
   export UPLOAD_PORT=none
   make V=1 NO_UPLOAD=1 NO_RUN=1