extend masterrun to build sac2c with/without various features

This issue was spawned from the MR !43 (merged) which made it evident that we need to extend the masterrun to build sac2c with or without various combinations of features. This should hopefully more quickly reveal problems like the one solved by the MR.

It is unclear though what the best way of doing this is; either we extend .gitlab-ci.yml to build sac2c with different feature flags, or we run a few more docker images with various installs. Are there other possibilities?