buildx: rollback configuration if create fails

This builds on the added warnings from initialized builders, now
erroring the command, and additionally attempting to revert to the
previous configuration.

To preserve the previous configuration, we add a deep Copy() function to
the NodeGroup and Node so that we can easily restore it later if we
encounter a failure.

Signed-off-by: Justin Chadwell <me@jedevc.com>

store/nodegroup.go

@@ -110,6 +110,44 @@ func (ng *NodeGroup) Update(name, endpoint string, platforms []string, endpoints
 	return nil
 }
 
+func (ng *NodeGroup) Copy() *NodeGroup {
+	nodes := make([]Node, len(ng.Nodes))
+	for i, node := range ng.Nodes {
+		nodes[i] = *node.Copy()
+	}
+	return &NodeGroup{
+		Name:    ng.Name,
+		Driver:  ng.Driver,
+		Nodes:   nodes,
+		Dynamic: ng.Dynamic,
+	}
+}
+
+func (n *Node) Copy() *Node {
+	platforms := []specs.Platform{}
+	copy(platforms, n.Platforms)
+	flags := []string{}
+	copy(flags, n.Flags)
+	driverOpts := map[string]string{}
+	for k, v := range n.DriverOpts {
+		driverOpts[k] = v
+	}
+	files := map[string][]byte{}
+	for k, v := range n.Files {
+		vv := []byte{}
+		copy(vv, v)
+		files[k] = vv
+	}
+	return &Node{
+		Name:       n.Name,
+		Endpoint:   n.Endpoint,
+		Platforms:  platforms,
+		Flags:      flags,
+		DriverOpts: driverOpts,
+		Files:      files,
+	}
+}
+
 func (ng *NodeGroup) validateDuplicates(ep string, idx int) error {
 	i := 0
 	for _, n := range ng.Nodes {