Drp `poetrylock` and `pyproject` mandatory arguments
without default values and drops `src` from `mkPoetryPyhon`.
Fix test invocations with invalid arguments.
This adds the following new tests:
- trivial: minimaltest case
- override-support: verify overriding
- common-pkgs-1/2: verify commonly downloaded pypi pkgs can be built
Also adds some overrides as needed by some of the
tested packages.
