release -> user upgrade test issue

[Jonathan Riddell]

user snapshotting is broken again because the release upgrade test won't succeed

http://build.neon.kde.org/view/mgmt/job/mgmt_daily_promotion_xenial_release/117/console

It has a problem upgrading some combination of these packages

bzr-builddeb germinate libgpgme11 pkg-kde-tools python-apt
python-apt-common python-gpgme python3-apt python3-germinate
python3-software-properties software-properties-common
ubuntu-dev-tools unattended-upgrades

but I can't understand its output to work out what it is nor recreate
the problem locally

software-properties we used to build and then removed from archive and
added /etc/apt/preferences.d/99-neon-software-properties to prefer the
version from ubuntu archive

python-apt we build

I'm a bit stuck

Jonathan