Add integration test for stack deploy with secrets.

Signed-off-by: Daniel Nephin <dnephin@docker.com>

secret_update.go

@@ -8,8 +8,7 @@ import (
 	"golang.org/x/net/context"
 )
 
-// SecretUpdate updates a Secret. Currently, the only part of a secret spec
-// which can be updated is Labels.
+// SecretUpdate attempts to updates a Secret
 func (cli *Client) SecretUpdate(ctx context.Context, id string, version swarm.Version, secret swarm.SecretSpec) error {
 	query := url.Values{}
 	query.Set("version", strconv.FormatUint(version.Index, 10))