IntegrationTesterBase

Initializes the workspace in preparation for integration testing

Remove any ID files to try and force them to exit

The working directory of the integration test suite, which is the root of the Mill build being tested. Contains the build.mill file, any application code, and the out/ folder containing the build output

Each integration test that runs in the same baseWorkspacePath is given a new folder for isolation purposes; even though we try our best to clean up the processes and files from each Mill run, it still doesn't work 100%, and re-using the same folder can cause non-deterministic interference and flakiness