currently kube-controller-manager cannot run outside of a vm started
by openstack (with --cloud-provider=openstack params). We try to read
the instance id from the metadata provider or the config drive or the
file location only when we really need it. In the normal scenario, the
controller-manager uses the node name to get the instance id.
https://github.com/kubernetes/kubernetes/blob/41541910e1699975a8f9202a89b6865e45921194/pkg/volume/cinder/attacher.go#L149

The localInstanceID is currently used only in the test case, so let
us not read it until it is really needed.