Add tests and fix behavior of scanner cli
- add smoke and unit tests for cli to have maximum coverage
- fix behavior of cli in case an invalid config file is specified via envvar
- rename scan to do_scan in scanner
- fix not self-contained temp_path fixture in conftest
Need advice on whether to use a real (tree that exist in the archive) root_path for the tests, here do_scan is mocked and never actually called.
Follow-up to !31 (closed).
Related to !31 (closed), D4130
Migrated from D4089 (view on Phabricator)