add manifest command

Enable inspection (aka "shallow pull") of images' manifest info, and
also the creation of manifest lists (aka "fat manifests").

The workflow for creating a manifest list will be:

`docker manifest create new-list-ref-name image-ref [image-ref...]`
`docker manifest annotate new-list-ref-name image-ref --os linux --arch
arm`
`docker manifest push new-list-ref-name`

The annotate step is optional. Most architectures are fine by default.

There is also a `manifest inspect` command to allow for a "shallow pull"
of an image's manifest: `docker manifest inspect
manifest-or-manifest_list`.

To be more in line with the existing external manifest tool, there is
also a `-v` option for inspect that will show information depending on
what the reference maps to (list or single manifest).

Signed-off-by: Christy Perez <christy@linux.vnet.ibm.com>
Signed-off-by: Daniel Nephin <dnephin@docker.com>

cli/command/commands/commands.go

@@ -8,6 +8,7 @@ import (
 	"github.com/docker/cli/cli/command/config"
 	"github.com/docker/cli/cli/command/container"
 	"github.com/docker/cli/cli/command/image"
+	"github.com/docker/cli/cli/command/manifest"
 	"github.com/docker/cli/cli/command/network"
 	"github.com/docker/cli/cli/command/node"
 	"github.com/docker/cli/cli/command/plugin"
@@ -39,12 +40,15 @@ func AddCommands(cmd *cobra.Command, dockerCli *command.DockerCli) {
 		image.NewImageCommand(dockerCli),
 		image.NewBuildCommand(dockerCli),
 
-		// node
-		node.NewNodeCommand(dockerCli),
+		// manifest
+		manifest.NewManifestCommand(dockerCli),
 
 		// network
 		network.NewNetworkCommand(dockerCli),
 
+		// node
+		node.NewNodeCommand(dockerCli),
+
 		// plugin
 		plugin.NewPluginCommand(dockerCli),