KCI builds once b-series (18.04 LTS) development starts

[Rik Mills]

Once the b-series (18.04 development start we would have 4 active series
building on KCI. Xenial, Zesty, Artful and 'b-series'.

Since we already arguably generate too many builds at present, then I
propose that we retire builds for both Xenial and Zesty.

Rational for those:

Xenial - There is little that we are likely to backport to Xenial any
more with the help of KCI, and what individual packages we might can be
test built on a case by case basis. We already have some breakages with
Xenial builds due to difficult to backport dependencies, which is only
going to get worse with time. It would be a better use of time and
resources to concentrate on the upcoming next LTS.

Zesty - Similar to Xenial, there is little now that we would with to
backport for Zesty. We cannot/should not backport 18.04 versions in the
backports ppa, as this would break Zesty -> Artful upgrades via the
release upgrader when a user had the backports ppa packages installed.
Zesty also only has 3 months worth of life once Artful is released, so
it will be going away soon anyway.

Thoughts/opinions please?

Regards

Rik Mills