Make cookbook/benchmark validation more robust

[gassmoeller]

#5259 is failing because the cookbook/benchmark validation is not very robust concerning different path layouts. Make the test more robust:

• automatically build all plugins in all subdirectories of the given cookbook/benchmark
• by default try to run all .prm files in all subdirectories (except for doc/)
• remove all special rules that are no longer necessary

@tjhei: can you take a look?

[tjhei]

I am ok with building all plugins, no harm here.

I am not sure your other changes will work: in CI we only validate and not run all examples. For running, many special cases are necessary (files use resume features, others don't converge, etc).

[tjhei]

Are you sure this works? I vaguely recall that the other prm files resume this file.

[gassmoeller]

Hmm, I guess you are right, I didnt try running the benchmarks. Let me think about this, maybe I split the PR up into the part dealing with plugins and the part dealing with prms.

[gassmoeller]

I think this will get too complicated to be worth the effort. Closing for now, we can revisit if necessary.