Use new libzypp callbacks

[lslezak]

Problem

• No installation progress with new libzypp
• https://bugzilla.suse.com/show_bug.cgi?id=1244319

Solution

• Use the new install callbacks
• Use also the download callbacks, now the default download mode is "downloadInAdvance" (first download all needed packages, the install them at once) so we need to show the progress for the download stage otherwise there would be no progress for quite some time as reported in the bug.

Testing

• Tested manually
• A testing installation ISO is built in the systemsmanagement:Agama:branches:new_libzypp_callbacks OBS project, the ISO can downloaded here

Screenshots

Note: The total number (1504 in this case) is not a number of packages to install but the total number of download and install steps. The remote packages are counted twice, the local packages only once. (But see the note below.)

That's just for simplification, I didn't have time to fix it.

Notes

• Currently it is not possible to abort a running package installation and if there is a problem during installation there is no retry (limitation of the current libzypp).

TODO

• Fix the failing unit tests
• Add a dependency to the new version of the pkg-bindings
• Test with offline (Full) medium, I'm not sure if the packages are also copied from the DVD and if the download callbacks are also used for that. In that case we would need to count the download also for the local packages. (Or ask the libzypp maintainers.)
• Count the downloads and installs separately to provide better progress (can be done later for RC3)
• Changes 😃