Handle packages which depend on LXC
Packages which depend on lxc fail to install dependencies in the GitLab docker images as the two are incompatible.
LAVA provides a mocker package which can satisfy the dependency, https://packages.debian.org/unstable/lava-lxc-mocker, which could be installed in the GitLab docker images by default to satisfy the dependency so that tests like piuparts can complete. Alternatively, an equivs package can be created and installed by default.
This prevents some packages which successfully complete piuparts in Debian from using the piuparts test in Salsa.