Comment 0 for bug 1926208

[Impact]
When users are looking at MOTD messages, they might find the text confusing, since we don't explicitly say that the security updates count are taking into consideration both standard security pockets and ESM pockets.

[Test Case]
1. Launch the following old version of a xenial container:
   lxc launch ubuntu:f4c4c60a6b752a381288ae72a1689a9da00f8e03b732c8d1b8a8fcd1a8890800 dev-x

2. Run apt update and install the updated version of update-notifier-common
3. Add the ubuntu-advantage-tools ppa:
   https://code.launchpad.net/~ua-client/+archive/ubuntu/daily
4. Install ubuntu-advantage-tools
5. Install the latest version of uaclient from the stable ppa:
   https://launchpad.net/~ua-client/+archive/ubuntu/stable/
6. Comment out all mentions of xenial-security/xenial-updates in /etc/apt/source.list
7. Run apt update
8. Install libkrad0:
   apt install libkrad0=1.13.2+dfsg-5
9. Run /usr/lib/update-notifier/apt-check --human-readable
10. See a message like this:

UA Infra: Extended Security Maintenance (ESM) is not enabled.

UA Infra: Extended Security Maintenance (ESM) is enabled.

3 packages can be updated.
1 of these updates is fixed through UA Infra: ESM.
1 of these updates is a security update.
To see these additional updates run: apt list --upgradable

To verify that the error is fixed:

1.Perform all the stages above until step 8
2 Install the new update-notifier from this ppa:
  https://launchpad.net/~lamoura/+archive/ubuntu/update-notifier-test-ppa
3. Run /usr/lib/update-notifier/apt-check --human-readable
4. See a message like this:
UA Infra: Extended Security Maintenance (ESM) is enabled.

4 updates can be installed immediately.
1 of these updates are UA Infra: ESM security updates.
To see these additional updates run: apt list --upgradable

That is now correct.

[Where problems could occur]

The changes in this package should only be seen when MOTD is getting a new message. If that script fails for some reason, it seems that MOTD will only not present the message, which is doesn't seem to be a system critical issue. Additionally, we would potentially have tracebacks in the update-notifier logs. Finally, if the logic is also incorrect, we would be displaying incorrect standard security messages to the user.

[Discussion]
Currently, we treat the upgrades coming from standard security pocket and ESM service with the same packaging count. This could be confusing, since we don't point that out in the current message that we have:

5 updates can be installed immediately.
5 of these updates are provide through UA Infrastructure ESM
5 of these updates are security updates

We believe this will be better if the message stated:
5 updates can be installed immediately.
5 of these updates are provide through UA Infrastructure ESM

And if we had a situation like that:

10 updates can be installed immediately.
5 of these updates are provide through UA Infrastructure ESM
8 of these updates are security updates

We would change it to:

10 updates can be installed immediately.
5 of these updates are provide through UA Infrastructure ESM
3 of these updates are standard security updates