logilab-common #298387 add a main entry point for pytest [done]

Something that would be useful as:

python -m logilab.common.pytest

currently, the only way to achieve this is through: python -c from logilab.common import pytest; pytest.run() which is quite ugly.

The motivation behind this is to be able to run pytest using a specific python interpreter (and not be bound the shebang in the pytest script), typically one from a virtualenv.