We are going to do fixes and enhancements to YAML loading processes. Move
corresponding code to one place before that as the preparatory step.

Place new utility in new test/test.py file - with MultiRU that will be the
place for tests of generic mode and test.jinja2.py, which will be renamed to
test_ors.py, will be using utilities from there. So place the utility into new
place from the start.

/cc @jhuge, @lu.xu, @tomo, @xavier_thompson, @Daetalus
/proposed-for-review-on nexedi/slapos!1526
/reviewed-by TrustMe