The current conf.get_config() function already handles loading from ENV.
Also, always use osc.build.calculate_build_root() instead of making a custom variable substitution.

…vm types

To avoid filesystem permission collisions with the builds using su_wrapper,
use an alternative buildroot path that appends username to '/var/tmp/build-root' for the rootless builds.

…uild and osc --vm-type option

…d tool