Allow `docker deploy` command accept filename with/without extension

This fix tries to address the issue raised in 25855 where the command
`docker deploy` can only accept a STACK without extension of `.dab`.
In other words, `docker deploy hellojavaee.dab` gives an error:
```
Bundle hellojavaee.dab.dab not found. Specify the path with --file
```

This fix updates the way namespace STACK is taken so that in case
`STACK.dab` is provided with `docker deploy`:
```
$ docker deploy STACK.dab
```
The `STACK` is used as namespace (instead of `STACK.dab`).

NOTE: This fix will only allows `.dab` extension in namespace, because
it is not possible to have a namespace with `.` in the middle. In other
words, a namespace `hello.java.ee` will not work anyway (whether the file
`hello.java.ee` exists or not).

An additional integration test has been added to cover the changes.

This fix fixes 25855.

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

command/stack/deploy.go

@@ -4,6 +4,7 @@ package stack
 
 import (
 	"fmt"
+	"strings"
 
 	"github.com/spf13/cobra"
 	"golang.org/x/net/context"
@@ -34,7 +35,7 @@ func newDeployCommand(dockerCli *command.DockerCli) *cobra.Command {
 		Short:   "Create and update a stack from a Distributed Application Bundle (DAB)",
 		Args:    cli.ExactArgs(1),
 		RunE: func(cmd *cobra.Command, args []string) error {
-			opts.namespace = args[0]
+			opts.namespace = strings.TrimSuffix(args[0], ".dab")
 			return runDeploy(dockerCli, opts)
 		},
 	}