Better config prometheus output

[tibz7]

When running the task Configure prometheus, the task might fail if there is a validation error.... but that error is just hidden to the user running the playbook!
So the only hack i ve found was changing the value to true in the task.... Which not the way to go.
I also tried to export env=CI in my env but without luck.

Also it is quite anoying that when running ansible with the check_mode everything looks good, but while running it for real it fails! Would it be possible to run promtool check against a temporary file or something like that, so it fails and report the error in check mode?