sanity: test NOT_FOUND on Node(Un)StageVolume

According to the CSI spec, a plugin must return a `NOT_FOUND` error when
`NodeStageVolume` or `NodeUnstageVolume` is called with a `volume_id` of
a volume that does not (or no longer?) exist.

The `sanity` package has tests asserting these `NOT_FOUND` reports for
various RPC calls, including `NodePublishVolume` and
`NodeUnpublishVolume`, but not for `NodeStageVolume` and
`NodeUnstageVolume`. This patch adds them for completeness.

See: https://github.com/container-storage-interface/spec/blob/87a27a2496565857ed564284eaa762587feb9453/spec.md#nodestagevolume-errors
See: https://github.com/container-storage-interface/spec/blob/87a27a2496565857ed564284eaa762587feb9453/spec.md#nodeunstagevolume-errors

Author: NicolasT

pkg/sanity/node.go

@@ -487,6 +487,25 @@ var _ = DescribeSanity("Node Service", func(sc *TestContext) {
 			Expect(serverError.Code()).To(Equal(codes.InvalidArgument))
 		})
 
+		It("should fail when the volume is missing", func() {
+			_, err := c.NodeStageVolume(
+				context.Background(),
+				&csi.NodeStageVolumeRequest{
+					VolumeId:         sc.Config.IDGen.GenerateUniqueValidVolumeID(),
+					VolumeCapability: TestVolumeCapabilityWithAccessType(sc, csi.VolumeCapability_AccessMode_SINGLE_NODE_WRITER),
+					PublishContext: map[string]string{
+						"device": device,
+					},
+					StagingTargetPath: sc.StagingPath,
+				})
+			Expect(err).To(HaveOccurred())
+
+			serverError, ok := status.FromError(err)
+			Expect(ok).To(BeTrue())
+			Expect(serverError.Code()).To(Equal(codes.NotFound))
+
+		})
+
 		It("should fail when no volume capability is provided", func() {
 
 			// Create Volume First
@@ -582,6 +601,20 @@ var _ = DescribeSanity("Node Service", func(sc *TestContext) {
 			Expect(ok).To(BeTrue())
 			Expect(serverError.Code()).To(Equal(codes.InvalidArgument))
 		})
+
+		It("should fail when the volume is missing", func() {
+			_, err := c.NodeUnstageVolume(
+				context.Background(),
+				&csi.NodeUnstageVolumeRequest{
+					VolumeId:          sc.Config.IDGen.GenerateUniqueValidVolumeID(),
+					StagingTargetPath: sc.StagingPath,
+				})
+			Expect(err).To(HaveOccurred())
+
+			serverError, ok := status.FromError(err)
+			Expect(ok).To(BeTrue())
+			Expect(serverError.Code()).To(Equal(codes.NotFound))
+		})
 	})
 
 	Describe("NodeGetVolumeStats", func() {