One node can be allocated to only one user

[Shimmer93]

Issue: Even when a user has only requested 1 cpu or 1 gpu and more resources are available, other users can't apply to the same node.

Reproduce: In tuxiv.conf:

job:
    name: test
    general:
      - nodes=1
      - ntasks=1
      - cpus-per-task=1
      - gres=gpu:1

Expected behavior: Node 1 has 39 CPUs and 7 GPUs available, and other users can use the rest of resources