Isolate test omc to only have tools a user would have installted #356

Currently we build OMC from scratch while a user would usually install OpenModelica via the package manager.
This means we have more tools available that a user might not have and we don't know if the install scripts doesn't copy some required files into the package versions.

Tasks

Things we should try to support:

1. Install OpenModelica nightly and run library testing with that version.
2. Build OpenModelica master (or PR branch) using CMake in a build-deps Docker image. Copy the install directory into a separate "clean" container.