use jenkins file for spack PR

[cosunae]

so that we can parametrized and better maintain it.
The idea is that you can specify a SPEC parameter, and will trigger a specific build of spack.
But if not, the default behaviour would be to build a set of predefined tests: cosmo, icon, int2lm, etc.
for dummy users that are not sure what should be tested for validating a spack PR

[dominichofer]

done