Validate stack-names for empty values

Add validation for stack names to prevent an empty name resulting in _all_
stacks to be returned after filtering, which can result in removal of services
for all stacks if `--prune`, or `docker stack rm` is used.

Before this change;

    docker stack deploy -c docker-compose.yml one
    docker stack deploy -c docker-compose.yml two
    docker stack deploy -c docker-compose.yml three

    docker stack deploy -c docker-compose.yml --prune ''
    Removing service one_web
    Removing service two_web
    Removing service three_web

After this change:

    docker stack deploy -c docker-compose.yml one
    docker stack deploy -c docker-compose.yml two
    docker stack deploy -c docker-compose.yml three

    docker stack deploy -c docker-compose.yml --prune ''
    invalid stack name: ""

Other stack commands were updated as well:

Before this change;

    docker stack deploy -c docker-compose.yml ''
    Creating network _default
    failed to create network _default: Error response from daemon: rpc error: code = InvalidArgument desc = name must be valid as a DNS name component

    docker stack ps ''
    nothing found in stack:

    docker stack rm ''
    Removing service one_web
    Removing service three_web
    Removing service two_web

After this change:

    docker stack deploy -c docker-compose.yml ''
    invalid stack name: ""

    docker stack ps ''
    invalid stack name: ""

    docker stack rm ''
    invalid stack name: ""

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

cli/command/stack/swarm/remove.go

@@ -16,12 +16,15 @@ import (
 
 // RunRemove is the swarm implementation of docker stack remove
 func RunRemove(dockerCli command.Cli, opts options.Remove) error {
-	namespaces := opts.Namespaces
+	if err := validateStackNames(opts.Namespaces); err != nil {
+		return err
+	}
+
 	client := dockerCli.Client()
 	ctx := context.Background()
 
 	var errs []string
-	for _, namespace := range namespaces {
+	for _, namespace := range opts.Namespaces {
 		services, err := getStackServices(ctx, client, namespace)
 		if err != nil {
 			return err