Update to 6.6.0

The packaging part is unexciting and done, however while testing I quickly realized that there's a regression that hits installations that are using plain partitioning instead of LVM.

This is the same issue I mentioned a few days ago: unfortunately, at the time I mistakenly thought 6.6.0-rc1 fixed the issue, when in reality what was happening is that the issue was introduced after 6.6.0-rc1, which is why I couldn't reproduce it with that version.

I've reported the issue upstream, hopefully it won't take too long for someone to come up with a solution: once that's done, we can backport the fix and upload 6.6.0 to the archive.

Feel free to provide feedback on everything else in the meantime.