Details: Update the command 

From

oc create secret generic ssh-key-secret \
  -n openshift-sandboxed-containers-operator \
  --from-file=id_rsa.pub=./id_rsa.pub

To

oc create secret generic ssh-key-secret \ -n openshift-sandboxed-containers-operator \ --from-file=id_rsa.pub=./id_rsa.pub \ --from-file=id_rsa=./id_rsa

Documentation URL: Creating the KVM host secret