Find something reusable for download + verify + extract

[solsson]

We do the same curl + untar operation all the time, basically with paramters URL and destination path. We sometimes verify checksums properly, sometimes not.

Others have made the same observation:

• https://github.com/JosuaKrause/curl-chk
• https://github.com/mmikulicic/runck
• https://github.com/antoineco/curl-check-install

[solsson]

Stumbled upon this function from the kubernetes community:
https://github.com/kubernetes/ingress-nginx/blob/0.9.6/images/nginx-slim/build.sh#L37