Use pbuilder in CI

[rvem]

Clarification and motivation

After #60 we'll have proper package generation for ubuntu.
We want to be sure that source packages generated inside docker container are sane. One way to do that
is to build them using pbuilder.

Acceptance criteria

CI runs pbuilder for at least one source package to test the building.

[rvem]

pbuilder-dist sources: https://code.launchpad.net/~ubuntu-dev/ubuntu-dev-tools/+git/ubuntu-dev-tools

[krendelhoff]

Why not consider to use it instead of dpkg-buildpackage?

[rvem]

AFAIR, my initial goal was to check that built source packages can be built on the launchpad without submitting builds to it, and pbuilder-dist simulates launchpad builders quite well

[krendelhoff]

But it also actually builds the binary

[krendelhoff]

Users who currently build binary debs with just debuild are strongly encouraged to consider how their build process might be modified to support the use of pbuilder.

[rvem]

Is it possible to build a source package (aka .orig.tar.gz, debian.tar.xz, .dsc and .changes files) using pbuilder?

[krendelhoff]

AFAIU, no, only binary

[rvem]

As for building binary packages, I think it's a good idea to update test deb binary packages via docker step to use pbuilder instead of dpkg-buildpackage