redhat_subscription: use CLI when using environments (#6319)
It turns out that the 'environments' that the D-Bus Register*() APIs
accept are the IDs of the environments, and not the user-facing names of
the environments (which is what the module has been accepting so far).
Since there is no easy way to do the mapping manually, for now use again
the subscription-manager CLI for registering when environments are
specified.
(cherry picked from commit 83994c0a2d)
Co-authored-by: Pino Toscano <ptoscano@redhat.com>
