Make tests faster by skipping Modelica libraries
A lot of time was spent in Pymoca's transfer_model to compile the model. That is because since d1bc9d42 we have RTC-Tools Channel Flow as a dependency, so we would parse its entire library again for every model.
The RTC-Tools tests do not need any RTC-Tools Channel Flow components (or other libraries for that matter), only the examples do. Therefore, we can explicitly disable additional library folders using the compiler_options() method to make compilation of a model much faster.