Whole new version of OSPurge. This new version is: * Faster (multithreaded, thanks to a ThreadPoolExecutor) * Safe (we check and wait for some prerequisites before attempting a delete) * 100% unit tested. * Modular (one file per service) Note that it's Python3.5 compatible. It also uses OpenStack Shade and OpenStack client-config libraries so that OSPurge focuses on the cleaning logic only.