adding archlinux support

This requires a change in init.pp so it allows empty (false) $package value
without throwing an error. This is because locale generation binaries and
configuration files belong to glibc package. Allowing to control autoupgrade of
such essential system package via `locales` addon can cause too much undesired
behaviour so I have added logic which runs autoupdate only if $package != false.

Otherwise this commit adds params.pp changes to reflect archlinux system. There
is no $locale_update_cmd as there seems to be no userspace tools to reload
locale without rebooting.