Configuration option to force use of system site-packages

• I have searched the issues of this repo and believe that this is not a duplicate.
• I have searched the documentation and believe that my question is not covered.

Feature Request

We need a way to tell poetry to ignore the currently active virtual environment. I am running into a roadblock trying to automate some of the poetry install operations from python.

As a comparison, pipenv supports it through the PIPENV_IGNORE_VIRTUALENVS environment variable.

The best approach, I think, is a switch like --breakout-of-venv (can't find a good name) to tell poetry to ignore the currently activated environment for any command that needs to deal with the virtual environment (install, add, remove...).

Other ideas:

• It feels like poetry env is the right candidate for this. Something like poetry env use --default maybe. But then you always need 2 commands per poetry command if you're using e.g. subprocess.call() to make it work; only useful in a real CLI context.
• A poetry config could work, but it sounds weird to modify this in order to run a script.
• An env variable -only solution like pipenv does is cumbersome and annoying to use, but having the option to do it is useful for CI servers.

Start by tracing how Poetry's install, add, remove, and env commands choose an environment, then compare the requested behavior with PIPENV_IGNORE_VIRTUALENVS. Determine whether the completed change should be a switch, configuration setting, or environment variable, and verify that activated virtual environments are ignored for the affected operations.