python-dev will be depreciated in Focal but can be used as python2-dev
so removed it from common dockerfile.template and added it
as an extra package in .circleci/config.yml.
Injecting the generated-file warning into the settings dict felt a
little unnecessarily magical. A warning like this is always going
to be at the top; the way it might differ between files is mainly
if the syntax for a comment varies, and in that case a simple
substitution like we're doing in this template wouldn't be enough
to express the difference anyway. So, embrace the hardcoding.
Now, the template and the images.yml entry have a very simple
relationship: the keys in one are exactly the keys in the other.
That's good for people quickly and confidently understanding it.
arpit551
Anders Kaseorg
Aditya Bansal
Greg Price
Vishnu Ks