tests: add Balto configuration file I have been developing a Mercurial test runner plugin for being able to run Mercurial tests with Balto (https://bitbucket.org/lothiraldan/balto/src/default/). Balto requires a configuration file so let's include it, I have added the required information in the configuration file as comments. I hope Balto would be an helpful tool for other people than me. Differential Revision: https://phab.mercurial-scm.org/D5283