Synchronize common files from prometheus/prometheus

[prombot]

Propagating changes from prometheus/prometheus default branch.

Source can be found here.

To check out this branch locally and push changes back:

git remote add prombot https://github.com/prombot/prometheus_prom2json.git
git fetch prombot repo_sync
git checkout -b repo_sync prombot/repo_sync