Split docker makefile in toolchain build and firmware build

[ccinelli]

This PR include:

• Fix for docker built. The current docker build process is broken (see Fix docker build #329).
• Add tests for the docker build (so breaking changes will not go unnoticed again).
• Separate building the toolchain and building the firmware. Currently the flow with docker is a little messy. Dockerfile installs everything except the solo-python. At the same time checkout again the code inside the container. So in order to build the firmware we have to push the code to origin. This PR uses Docker to build a toolchain container that can build the firmware but use the code on the local machine. This is done mapping the main repo inside /solo in the container. make docker-build-toolchain builds the toolchain and make docker-build-all builds all the different type of the firmware.
• Put the definition of VERSION_FULL in one place and remove the dependency on GIT in the docker. In multiple makefiles git describe is used to decide the version of the firmware. It is better to do this only once in the main Makefile and pass the version (VERSION_FULL) to the other makefiles.
• The current docker file is unoptimized and end up creating unused files in layers. This PR bring the final docker image down from about 1.2GB to 890Mb. It creates only 4 layers following docker best practices:
  • The apt packages (cleaning the cache after installing)
  • The ARM compiler
  • Python 3.7 (miconda)
  • solo-python python package
• Update the ARM toolchain to the latest one: 8-2019-q3
• Add the .sha2 files to .gitignore
• It adds makefile update to download the latest firmware from master

You can test it by running make docker-build-toolchain and make docker-build-all

[conorpp]

Thank you!

[conorpp]

@all-contributors please add @ccinelli for infrastructure, tests

[allcontributors]

@conorpp

I've put up a pull request to add @ccinelli! 🎉