kube-up: Only specify ETCD_QUORUM_READ if non-empty

Fix kubernetes#38290

cluster/gce/configure-vm.sh

@@ -458,7 +458,6 @@ num_nodes: $(echo "${NUM_NODES:-}" | sed -e "s/'/''/g")
 e2e_storage_test_environment: '$(echo "$E2E_STORAGE_TEST_ENVIRONMENT" | sed -e "s/'/''/g")'
 kube_uid: '$(echo "${KUBE_UID}" | sed -e "s/'/''/g")'
 initial_etcd_cluster: '$(echo "${INITIAL_ETCD_CLUSTER:-}" | sed -e "s/'/''/g")'
-etcd_quorum_read: '$(echo "${ETCD_QUORUM_READ:-}" | sed -e "s/'/''/g")'
 
 hostname: $(hostname -s)
 enable_default_storage_class: '$(echo "$ENABLE_DEFAULT_STORAGE_CLASS" | sed -e "s/'/''/g")'
@@ -495,6 +494,11 @@ EOF
     else
       cat <<EOF >>/srv/salt-overlay/pillar/cluster-params.sls
 etcd_over_ssl: 'false'
+EOF
+    fi
+    if [ -n "${ETCD_QUORUM_READ:-}" ]; then
+      cat <<EOF >>/srv/salt-overlay/pillar/cluster-params.sls
+etcd_quorum_read: '$(echo "${ETCD_QUORUM_READ}" | sed -e "s/'/''/g")'
 EOF
     fi
     # Configuration changes for test clusters