Update path for "parallel" package

Update path for "parallel" package

The old URL is no longer reachable, causing build failures for packer
builds.

Molecule requirement has been changed to "molecule[docker]", due
to a breaking change introduced in molecule 3.1.1, where docker was
moved out of the default module.

rpm_key blocks added for direct installs of packages in CentOS 8, as
not having these GPG keys in place is now an error condition.

Issue: IT-20979
Change-Id: I837419c2cd92f0ec19849f0a4da3ec5c36b2cb5e
Signed-off-by: Eric Ball <eball@linuxfoundation.org>