gnu: Add slurm.

* gnu/packages/parallel.scm (slurm): New variable.
* gnu/packages/patches/slurm-configure-remove-nonfree-contribs.patch:
  New file.
* gnu-system.am (dist_patch_DATA): Add it.
* gnu/packages/parallel.scm: Introduce license name space.

Co-authored-by: Andreas Enge <andreas@enge.fr>