client upgrade from py2 -> py3 does not report status of any in progress activities

[Chad Smith]

Found this while testing upgrade path from py2 -> py3 of landscape-client.

steps to reproduce:

1. register a bionic or artful landscape-client py2 to talk to your racecar or hosted server.
2. After client reports all packages to your landscape server,
attempt to apply a simple package profile (which is broken on py2 currently).

3. Wait for queued activity to go "in progress" from landscape server UI/API.
   - Activity will fail due to apt-secure not liking an untrusted local apt repo
    - Traceback in /var/log/landscape/package-changer.log on the client

4. make package on tip of master
5. dpkg -i the py3 lanscape-common and lanscape-client you just built
6. see your package profile apply after next exchange 'dpkg -l | grep landscape | grep profile'
7. See that landscape-client (py3) thinks secure_id changed
    - grep secure /var/log/landscape/broker.log
   'Response message with operation-id <your profile activitiy id> was discarded because the client's secure ID has changed in the meantime.

I added a debug log to landscape/client/broker/exchange.py:_message_is_obsolete and sure enough
bytes versus string comparison issues
self._registration_info.secure_id is bytes and context.secure_id is a string.

[Simon Poirier (simpoir)]

https://github.com/CanonicalLtd/landscape-client/pull/35