allow dockerfile to set the port for the flask application

[kymwatts]

Hello,

in some cases, loading the docker container into a preexisting cluster can cause port conflicts.
Can you setup the flask app.py to use an environment variable for setting the port.

Is it possible to make these 2 changes:
app.py:
line 556
port = int(os.environ.get('FLASK_PORT','8080'))

Dockerfile:
line 20
ENV FLASK_PORT 8081
EXPOSE 8081

This way we can set a different port to launch the application on.

Cheers
Kym