Fix a syntax error in the validation script. Before this change, the
script would not detect, and thus error, on an endpoint with a schema
that is not HTTP and not HTTPS.
Before this change the validation steps, and the script, assumed that
`internal` and `admin` OpenStack endpoints were always reachable. With
this change, the manual steps and the script are amended to only check
the validity of HTTPS certificates on the `public` endpoints of the
OpenStack catalog.
Provide manual instructions to check the HTTPS certificates of the
OpenStack endpoints for systems where the required tools for the
provided script aren't available.
