Update eoan with landscape-client 19.12

[Simon Poirier]

[Impact]

Reference:
https://wiki.ubuntu.com/StableReleaseUpdates#New_upstream_microreleases

This SRU is for the 19.12 release of landscape-client which includes:

 * Modernized packaging.
 * Added support for python-apt 1.9
 * Converted init script to systemd service.
 * Sysinfo: add support for multiple IPv6 addresses per interface. (LP: #829379)
 * Upstream version of previous SRU patches.

[Test Case]

 * There is no specific test cases for this since it's an upstream release including all
   previously patched bugfixes, along with with a few regression fixes due to new versions
   present in eoan.

 * The current unit test suite and system test suite now pass on eoan/focal.
   (e.g. https://travis-ci.org/CanonicalLtd/landscape-client/builds/620310386)

 * The updated packaging also adds build-time testing, which should help raise regressions faster
   in the future.

[Regression Potential]

 * Most of the changes, apart from the ones listed above have been patched through SRU and are
   already proven.

 * The init.d to systemd update is a potential regression point. In the event there were any
   issues with this change, the effect would be fairly apparent since landscape-client relies
   on it for startup. However, the new service configuration is much simpler than previously.

 * Another potential regression point is the update python-apt support. It changed package
   profiles enforcement. As the feature was completely broken, any regression would likely
   affect edge cases in package profiles which were not already covered by current test suites.

[Eric Desrochers (slashd)]

A current landscape-client SRU (LP: #1855522) prevents me to upload 19.12 in the archive.

Let's circle back in Jan 2020 for the sponsoring of 19.12 lds-client.

- Eric

[Brian Murray (brian-murray)]

The Eoan Ermine has reached end of life, so this bug will not be fixed for that release