run slurmctld as user

Notice: also trying to run slurmd on execute nodes as user makes no
sense because it breaks sbatch. Furthermore there is another necessary
to run mpi jobs (just tried MpiDefault=none). I don't consider running
slurmd as root a good idea, but there seems to be no other choice at the
moment.

roles/slurm/tasks/main.yml

@@ -82,6 +82,8 @@
     volumes: "{{default_mounts + ( item.extra_mounts | default([]) ) }}"
     networks:
     - name: "slurm"
+    env:
+      slurmuser: "{{slurm_user}}"
     image: "{{item.image}}"
     state: started
     detach: True