Gunicorn 25.1.0+ enables a 'control_socket' by default, which creates
a root-owned 'gunicorn.ctl' file in the chdir directory. When this
directory is a volume mount (as in our dev/test setups), it causes
permission errors during Docker build context gathering.
This change explicitly sets 'control_socket = None' to prevent the
creation of this file.
8c9d263afb