The previous version of Debcrafter didn't catch these mistakes. Now they
were discovered and fixed.

Verifying signatures is not that great because when the keys expire the
build is broken. We instead pin the packages while still being able to
verify when the pin is updated. This already has some keys expired so
the pins are added here.

The tests were previously running even when build failed which was
useless and wasteful. This switches it to run only on success.

CI was building packages one after another in a single VM. This is slow,
has the risk of one package affecting another and makes it harder to
figure out which job failed. This change adds a preparation job which
builds the image and gets the list of packages and changes build job
into matrix depending on the prepare job.

When a service fails to start the maintainerscript would only print a
help, not full log. This is annoying when testing in CI as there's no
way to do that and even in case of local tests it's just one more step.

This change adds a check that would print the log for service packages.
Although it won't show anything if the failure happened before starting,
this is OK, it's just debug info.

Previously imported files had to specified twice - in `build_rules` and
in `sps` files. This uses the new debcrafter feature to avoid it and
prepares for heavier CI caching.

`lnd-genmacaroon` doesn't use these, it's probably some copy-paste
mistake.

Previously caching was only implemented for container image building but
not for packages which still took a huge time to rebuild. This
implements caching so that packages that didn't change aren't rebuilt.