fix for determining correct RHCOS image to use
fix for determining correct RHCOS image to use

The current way the docs specify the image to use for a new MachineSet
is incorrect.  Users need to query an existing MachineSet to determine
the correct value to use for the `image:` field.

vikram-redhat/openshift-docs,vikram-redhat/openshift-docs,vikram-redhat/openshift-docs,vikram-redhat/openshift-docs,vikram-redhat/openshift-docs