ST-370 - GIve Kurt Cobain access to Syscore workers for cleaning up

Kurt Cobain will now be able to clean up worker nodes - once this WIP MR is merged.

Before it is marked as Ready (no longer WIP), the following must happen:

• code in the roles/ssh/kc_syscore_access.yml file should be reviewed;
• lines 43 and 47 must be uncommented;
• lines 42 and 46 must be deleted.