System methods to port:
 o is_nvre_installed
 o list_newer_installed_packages
 o list_older_installed_packages
 o obtain_reactivation_key
 o add_note
 o delete_systems
 o get_custom_values
 o set_custom_values
 o list_user_systems
 o list_groups
 o set_group_membership
 o list_child_channels
 o list_base_channels
 o set_base_channel
 o set_child_channels
 o list_packages
 o download_system_id
 o get_entitlements
 o upgrade_entitlement
 o list_latest_installable_packages
 o list_latest_upgradable_packages