[Bug 1769258] [NEW] Cope with unsupported kernel

[Andreas Hasenack]

Public bug reported:

Livepatch now checks for the running kernel and let's the user know if
it's unsupported. For example:

```
ubuntu at bionic-livepatch:~$ canonical-livepatch enable foo
2018/05/04 19:55:05 cannot use livepatch: your kernel "4.15.0-1008-kvm" is not eligible for livepatch updates
```


`ua status`, however, doesn't interpret that yet and just says that livepatch is disabled:
```
ubuntu at bionic-livepatch:~$ ua status
esm: disabled (not available)
fips: disabled (not available)
livepatch: disabled
```

Furthermore the MOTD component says that livepatch is available for installation, likely because the status output does not say "not available":
```
 * Canonical Livepatch is available for installation.
   - Reduce system reboots and improve kernel security. Activate at:
     https://ubuntu.com/livepatch
```

`ua enable-livepatch <foo>` also doesn't check and tries to enable it, but it eventually fails:
```
ubuntu at bionic-livepatch:~$ sudo ua enable-livepatch <token>
Enabling Livepatch with the given token, stand by...
2018/05/04 19:57:17 cannot use livepatch: your kernel "4.15.0-1008-kvm" is not eligible for livepatch updates
```

We should:

- fix the MOTD when running an unsupported kernel. I suggest to output nothing.
- don't even try to enable livepatch if we are running an unsupported kernel

** Affects: ubuntu-advantage-script
     Importance: Unknown
         Status: Unknown

** Affects: ubuntu-advantage-tools (Ubuntu)
     Importance: Undecided
         Status: New

** Bug watch added: github.com/CanonicalLtd/ubuntu-advantage-script/issues #142
   https://github.com/CanonicalLtd/ubuntu-advantage-script/issues/142

** Also affects: ubuntu-advantage-script via
   https://github.com/CanonicalLtd/ubuntu-advantage-script/issues/142
   Importance: Unknown
       Status: Unknown

-- 
You received this bug notification because you are a member of Ubuntu
Server, which is subscribed to ubuntu-advantage-tools in Ubuntu.
https://bugs.launchpad.net/bugs/1769258

Title:
  Cope with unsupported kernel

To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu-advantage-script/+bug/1769258/+subscriptions