Update from FCOS OKD 4.13 to SCOS OKD 4.13 fails with SDN failure

[peterroth]

I tried to update a test cluster from FCOS based OKD 4.13.0-0.okd-2023-05-22-052007 to SCOS based 4.13.0-0.okd-scos-2023-12-19-054611 but it failed. After 1 master and 1 worker restarted, the cluster operators were hanging for a long time. The sdn reported the following error in the openshift-sdn namespace:

   State:       Waiting
      Reason:    CrashLoopBackOff
    Last State:  Terminated
      Reason:    Error
      Message:   /bin/bash: line 49: RHEL_VERSION: unbound variable

The initial cluster was in its original form when I started the updated, no changes or additions were made.

[peterroth]

Just a small addition: it happened when the original, FCOS cluster was deployed with OpenShiftSDN.