Allow extra parameters to be provided to docker image

[halkeye]

• When you exec, it'll actually replace the process so signals get sent to it properly.
• Also added $@ so gunicorn flags can be added/changed for docker run

[coveralls]

Coverage remained the same at 86.43% when pulling 2ff0120 on halkeye:exec-and-wildcard into 80a691b on open-eats:master.

[RyanNoelk]

Thanks for the PR will test this out when I have some spare time 👍