[test] Add a pytest to test the default template directives

Hello @bdepaula , fyi: @agayayav

I think we are missing an important test, that it is just one that checks the default hpc directives that will be added in the job template.

In 4.1.8 ( patched ), I added the exclusive directive and tested when it is Exclusive: " and when it is Exclusive: True; this was not enough when the exclusive parameter is not defined.

So, to never forget that case for other parameters, I would just create a basic test that contains %jobs.job.a.platform%=(slurm,pjm...), check its template ( I would do the full process, so it includes the conversion of the values into the directives ) , and compare it with the expected default values. So it works in a general way.