fixes #10 fixes #16 fixes #17 Refactored calculations for container sizes.  Now everything is within 1-2% for both small and large archives, now that we are taking into account ext4 filesystem overhead as well as reserved space for root user.  Also made the cleanup() function idempotent so that it can safely be called for example when there is need to reprovision a container and it may not be known whether the container is mounted/mapped, but we need to make sure that it is unmounted/unmapped so we can safely recreate it.