All the credit goes to Wonderfall. Thanks for that!
See: https://github.com/Wonderfall/dockerfiles/issues/110

 - searx/settings.yml is the right name in second sed line
 - COPY requirements.txt . does not work: "Not a directory"

- Install new packages needed to deploy search
- Optimize dockerfile for more docker deamon caching
- Pin a python2.7 base image.