refactor: use variable to decide if we want slurm client

ansible/cheaha.yml

@@ -7,4 +7,4 @@
     - { name: 'cheaha.node', tags: 'cheaha.node' }
     - { name: 'nfs_mounts', tags: 'nfs_mounts' }
     - { name: 'ldap_config', tags: 'ldap_config' }
-    - { name: 'slurm_client', tags: 'slurm_client', when: "'proxy' not in group_names" }
+    - { name: 'slurm_client', tags: 'slurm_client', when: enable_slurm_client }

ansible/group_vars/all

@@ -4,6 +4,7 @@
   yum_repo_files: []
   pkg_list: []
   slurm_version: 18.08.9
+  enable_slurm_client: false
 
 # NHC related
   nhc_download_url: "https://github.com/mej/nhc/releases/download/1.4.3/lbnl-nhc-1.4.3-1.el7.noarch.rpm"