Embed DockerVersion in plugin config.

Embedding DockerVersion in plugin config when the plugin is created,
enables users to do a docker plugin inspect and know which version
the plugin was built on. This is helpful in cases where users are
running a new plugin on older docker releases and confused at
unexpected behavior.

By embedding DockerVersion in the config, we claim that there's no
guarantee that if the plugin config's DockerVersion is greater that
the version of the docker engine the plugin is executed against, the
plugin will work as expected.

For example, lets say:
- in 17.03, a plugin was released as johndoe/foo:v1
- in 17.05, the plugin uses the new ipchost config setting and author
publishes johndoe/foo:v2

In this case, johndoe/foo:v2 was built on 17.05 using ipchost, but is
running on docker-engine version 17.03. Since 17.05 > 17.03, there's
no guarantee that the plugin will work as expected. Ofcourse, if the
plugin did not use newly added config settings (ipchost in this case)
in 17.05, it would work fine in 17.03.

Signed-off-by: Anusha Ragunathan <anusha.ragunathan@docker.com>

api/swagger.yaml

@@ -1452,6 +1452,10 @@ definitions:
           - Env
           - Args
         properties:
+          DockerVersion:
+            description: "Docker Version used to create the plugin"
+            type: "string"
+            x-nullable: false
           Description:
             type: "string"
             x-nullable: false

api/types/plugin.go

@@ -42,6 +42,9 @@ type PluginConfig struct {
 	// Required: true
 	Description string `json:"Description"`
 
+	// Docker Version used to create the plugin
+	DockerVersion string `json:"DockerVersion,omitempty"`
+
 	// documentation
 	// Required: true
 	Documentation string `json:"Documentation"`

plugin/backend_linux.go

@@ -24,6 +24,7 @@ import (
 	"github.com/docker/docker/distribution"
 	progressutils "github.com/docker/docker/distribution/utils"
 	"github.com/docker/docker/distribution/xfer"
+	"github.com/docker/docker/dockerversion"
 	"github.com/docker/docker/image"
 	"github.com/docker/docker/layer"
 	"github.com/docker/docker/pkg/chrootarchive"
@@ -758,6 +759,8 @@ func (pm *Manager) CreateFromContext(ctx context.Context, tarCtx io.ReadCloser,
 		DiffIds: []string{layerDigester.Digest().String()},
 	}
 
+	config.DockerVersion = dockerversion.Version
+
 	configBlob, err := pm.blobStore.New()
 	if err != nil {
 		return err