Systems/Hosts: Katello 'Systems' should be named 'Content Hosts' in the CLI
All references to 'System' should be updated to 'Content Host' throughout the CLI. This include both input arguments as well as output.
fixes #5182 - Rename Systems to Content Hosts
This commit contains minor changes to rename Systems to Content Hosts
(i.e. system -> content-host). Note: although the command name is
changing, the CLI will continue to use the 'systems' API.
This commit does not address renaming System Groups as that will be