don't skip cert check for an example & use HTTPS

This changes two URLs from http to https and it fixes a Dockerfile to
stop skipping certificate validation. It also adds the ca-certificates
package to that Dockerfile example.

Docker-DCO-1.1-Signed-off-by: Cristian Staretu <cristian.staretu@gmail.com> (github: unclejack)
Merge pull request #4248 from unclejack/https_fixes

don't skip cert check for an example & use HTTPS