Vault 20270 docker test raft wal (#24463)

* adding a migration test from boltdb to raftwal and back
adding a migration test using snapshot restore

* feedback

sdk/helper/testcluster/docker/environment.go

@@ -1256,6 +1256,18 @@ COPY vault /bin/vault
 	return tag, nil
 }
 
+func (dc *DockerCluster) GetActiveClusterNode() *DockerClusterNode {
+	ctx, cancel := context.WithTimeout(context.Background(), 60*time.Second)
+	defer cancel()
+
+	node, err := testcluster.WaitForActiveNode(ctx, dc)
+	if err != nil {
+		panic(fmt.Sprintf("no cluster node became active in timeout window: %v", err))
+	}
+
+	return dc.ClusterNodes[node]
+}
+
 /* Notes on testing the non-bridge network case:
 - you need the test itself to be running in a container so that it can use
   the network; create the network using