Easily know if a Client is registered or not

Pull request is here https://github.com/CanonicalLtd/landscape-client/pull/103

(for any future travelers) I've come up with the following one-liner to detect whether the "landscape-client" is registered or not:

```bash
(python3 -c "from landscape.lib import bpickle; from landscape.client.broker.service import BrokerService; print('registered' if bool(bpickle.loads(open('/var/lib/landscape/client/{}.bpickle'.format(BrokerService.service_name), 'rb').read())['registration']['secure-id']) else 'not registered')" 2&>/dev/null && echo "registered") || echo "not registered"
```

It is basically a distilled version of the upstream patch, tested on bionic, focal, jammy, and kinetic. Could be used as a workaround until the feature lands.

The feature is landed already on the beta. I would recommend using the beta ppa. It is released for bionic, jammy, focal, and kinetic. sudo add-apt-repository ppa:landscape/self-hosted-beta

This bug was fixed in the package landscape-client - 23.02-0ubuntu1

---------------
landscape-client (23.02-0ubuntu1) lunar; urgency=medium

  * New upstream release 23.02:
    - Preventing the generation of large messages and logs that can overwhelm
      Landscape Server (LP: #1995775)
    - Improved MOTD slowdown on machines with many tap network interfaces
      (LP: #2006396)
    - No longer using deprecated apt-key when storing trusted GPG keys
      (LP: #1973202)
    - Fixed issue recognising Parallels VMs as Virtual Machine clients
      (LP: #1827909)
    - Fixes for incorrect logfile rotation config (LP: #1968189)
    - Client-side backoff handling to moderate traffic to Landscape Server
      during high load (LP: #1947399)
    - Avoid sending empty messages when catching up to expected next message
      (LP: #1917540)
    - --is-registered CLI option to quickly check if client is registered
      (LP: #1912516)
    - Can now report Ubuntu Pro attachment information if the version of
      Landscape Server it is registered to supports this (LP: #2006401)
    - Packages installed as dependencies as part of package profiles are now
      appropriately autoremovable (LP: #1878957)
    - Registration timeouts give an error instead of timing out (LP: #1889464)
    - RHEV hypervisor VMs are now recognized as virtual machines (LP: #1884116)
    - Doing a Landscape-driven release upgrade from a release running python 2
      to one running python 3 no longer hangs forever (LP: #1943291)

 -- Mitch Burton <email address hidden> Wed, 08 Feb 2023 10:23:31 -0800