title: pytest: environment variable to specify pytest.ini location
body: <p>How can I set an environment variable with the location of the <code>pytest.ini</code>, <code>tox.ini</code> or <code>setup.cfg</code> for running <code>pytest</code> by default?</p>
  
  <p>I created a docker container with a volume pointing to my project directory, so every change I make is also visible inside the docker container. The problem is that I have a <code>pytest.ini</code> file on my project root which won't apply to the docker container. </p>
  
  <p>So I want to set an environment variable inside the docker container to specify where to look for the pytest configuration. Does anyone have any idea how could I do that?</p>