Add ability to run build-simulator and test-format tests in Docker.

Syntax with local Docker image is:

docker run --rm -it -v ${PWD}:/sources --user $(id -u):$(id -g) infinitime-build /opt/test.sh build-simulator [repo branch]
docker run --rm -it -v ${PWD}:/sources --user $(id -u):$(id -g) infinitime-build /opt/test.sh test-format [commit]

The repo and branch parameters for build-simulator specify InfiniSim version to use for the test build.
The commit parameter for test-format specify base commit/branch/tag to compare against when testing the formatting.