tests/docker: add devicemapper storage test

Add a smoke test for the docker devicemapper storage backend.

Flatcar ships docker with support for the devicemapper storage back-end
but we don't test it regularly. This has almost lead to the docker 24
update silently shipping without that storage driver.

Signed-off-by: Thilo Fromm <[email protected]>

kola/tests/docker/docker.go

@@ -187,6 +187,30 @@ systemd:
 		Distros: []string{"cl"},
 	})
 
+	register.Register(&register.Test{
+		Run:         func(c cluster.TestCluster) { testDockerInfo("devicemapper", c) },
+		ClusterSize: 1,
+		Name:        "docker.devicemapper-storage",
+		// This test is normally not related to the cloud environment
+		Platforms: []string{"qemu", "qemu-unpriv"},
+		// Note: copied verbatim from https://github.com/coreos/docs/blob/master/os/mounting-storage.md#creating-and-mounting-a-btrfs-volume-file
+		// Added explicit btrfs driver selection because overlay2 is the default for btrfs FS in docker 23 and above
+		UserData: conf.Butane(`
+variant: flatcar
+version: 1.0.0
+
+storage:
+  files:
+  - path: /etc/docker/daemon.json
+    contents:
+      inline: |
+        {
+          "storage-driver": "devicemapper"
+        }
+`),
+		Distros: []string{"cl"},
+	})
+
 	register.Register(&register.Test{
 		// For a while we shipped /usr/lib/coreos/dockerd as the execstart of the
 		// docker systemd unit.