Description:
When envoy is run with --service-node and --service-cluster cli parameters the values are not respected when sending xDS DiscoveryRequests. If node element is present in the bootstrap file the values from bootstrap are sent, if node element is not present in bootstrap file node.id and node.cluster in DiscoveryRequest are empty.

Expected behavior is that value passed to --service-node is used as node.id in all DiscoveryRequests and --service-cluster is used as node.cluster.

Repro steps:
Given envoy is run with the following command
envoy --service-cluster cluster0 --service-node _Node_0 -c envoy.yaml
and node element is not present in envoy.yaml file, all xDS request are snet with following node definition:

Sending DiscoveryRequest for type.googleapis.com/envoy.api.v2.Cluster: node {
   build_version: "3f59fb5c0f6554f8b3f2e73ab4c1437a63d42668/1.7.0/Clean/RELEASE"
}