buildx: warn on editing nodes

Previously, editing nodes to contain a new set of driver options or
config files was unsupported, and silently dropping them. In this patch,
we update with these, as well as add a new warning message that any new
options may not taken into account until the builder restarts (which
may apply to the flags, platforms and endpoints as well).

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

commands/create.go

@@ -320,6 +320,9 @@ func createCmd(dockerCli command.Cli) *cobra.Command {
 }
 
 func csvToMap(in []string) (map[string]string, error) {
+	if len(in) == 0 {
+		return nil, nil
+	}
 	m := make(map[string]string, len(in))
 	for _, s := range in {
 		csvReader := csv.NewReader(strings.NewReader(s))