Adding deprecation message for token based discovery.

Token based discovery, which is the default discovery mechanism, will be
deprecated in release 1.2.8, and replaced by a new mechanism that is
backed by Docker Swarm mode.

Signed-off-by: Nishant Totla <nishanttotla@gmail.com>

cli/create.go

@@ -3,11 +3,14 @@ package cli
 import (
 	"fmt"
 	"log"
+	"os"
 
 	"github.com/docker/swarm/discovery/token"
 	"github.com/urfave/cli"
 )
 
+const tokenDeprecationErr = "Token based discovery is being deprecated in the next release (1.2.8).\nIt will be replaced by a default discovery backed by Docker Swarm Mode.\nOther mechanisms such as consul and etcd will continue to work.\n"
+
 func create(c *cli.Context) {
 	if len(c.Args()) != 0 {
 		log.Fatalf("the `create` command takes no arguments. See '%s create --help'.", c.App.Name)
@@ -18,5 +21,6 @@ func create(c *cli.Context) {
 	if err != nil {
 		log.Fatal(err)
 	}
+	fmt.Fprintf(os.Stderr, tokenDeprecationErr)
 	fmt.Println(token)
 }