Foreman » Installer

from https://github.com/theforeman/puppet-foreman/pull/974#pullrequestreview-711530448

As for other variables:

• version & plugin_version - I can still see a use case so I'm not entirely sure.
• user & group - these are hardly ever changed so I'd be in favor of moving them
• rails_env & app_root same
• vhost_priority same (perhaps even move it to apache.pp and only allow changing it via Hiera)