* CI: add no_proxy regression test
* proxy: Fix the no_proxy variable
Since 2.29, probably due to a change in ansible templating, the no_proxy
variable is rendered as an array of character rather than a string.
This results in broken cluster in some case.
Eliminate the custom jinja looping to use filters and list flatteing +
join instead.
Also simplify some things (no separate tasks file, just use `run_once`
instead of delegating to localhost)
