[cern] Trivial fix for cluster creation in master

cherry-pick https://review.opendev.org/#/c/679987/

This is the fix for the "line 528: KUBE_PROXY_ARGS: unbound variable" error in master.

Change-Id: Iaf5bbc8e4946c6625e82b6f68e754328f08b6ce7 Story: 2006492 Task: 36448

OS-9823