curtin/distro.py: add rocky as a RHEL-like variant
Rocky Linux declares ID_LIKE="rhel centos fedora" which causes
grub-install to install into "redhat" EFI vendor path. That is not
correct, as rocky variant should instead install into "rocky" EFI
vendor path. This is based on inspecting Rocky Linux grub &
rocky-release RPMs.
We are going to stop supporting Python 2 in future
development. There is plenty more stuff we can rip out as a
consequence of this but dropping it from CI is the first step and
unblocks other changes.
Make sure curthooks do not discard APT preferences
Although APT preferences applied properly when running curtin
apt-config, we observed during a full installation using Subiquity that
the preferences would not be honored when installing packages from the
"packages" autoinstall section.
This happened because the installation of packages occur after running
curthooks. Curtooks call handle_apt with an almost empty configuration.
Therefore, we would overwrite the preferences by removing the
etc/apt/preferences.d/90curtin.pref file.
It is to be noted that the same behavior occurs for the APT proxy.
Fixed by not removing etc/apt/preferences.d/90curtin.pref when the
configuration does not contain APT preferences.
* primary reason for this is to generate the changelog with a real
DEBNAME/DEBEMAIL
* remove template debian/changelog.trunk
* assume debian version 0ubuntu1
* let dch manage the changelog file
