title: Airflow configuration in environment variable not working
body: <p>I tried using ENV variable to configure connection urls, I have an ami that is preconfigured with alchemy_conn and broker_url etc, I have written environment variables to /etc/environment in the instances being spun up from the amis to override the properties in airflow.cfg file. I was able to access the variables from python code as well. </p>
  
  <p>But it doesn't seem to take effect while running ariflow, tried restarting the process as well but didn't work, it still points to the one in airflow.cfg file</p>