Sanity test requires NodeServiceCapability but CSI doesn't

[msau42]

CSI spec says the NodeServiceCapabilities is optional:

message NodeGetCapabilitiesResponse {
  // All the capabilities that the node service supports. This field
  // is OPTIONAL.
  repeated NodeServiceCapability capabilities = 1;
}

However, the sanity test fails if the node service returns 0 or nil node capabilities:

NodeUnpublishVolume [Node Server]
/usr/local/google/home/msau/workspace/go/src/sigs.k8s.io/gcp-filestore-csi-driver/vendor/github.com/kubernetes-csi/csi-test/pkg/sanity/node.go:232
  should fail when no volume id is provided [BeforeEach]
  /usr/local/google/home/msau/workspace/go/src/sigs.k8s.io/gcp-filestore-csi-driver/vendor/github.com/kubernetes-csi/csi-test/pkg/sanity/node.go:253

  Expected
      <[]*csi.NodeServiceCapability | len:0, cap:0>: nil
  not to be nil

[msau42]

/assign