Move api/client -> cli/command

Using
  gomvpkg
     -from github.com/docker/docker/api/client
     -to github.com/docker/docker/cli/command
     -vcs_mv_cmd 'git mv {{.Src}} {{.Dst}}'

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

command/plugin/cmd.go

@@ -0,0 +1,12 @@
+// +build !experimental
+
+package plugin
+
+import (
+	"github.com/docker/docker/cli/command"
+	"github.com/spf13/cobra"
+)
+
+// NewPluginCommand returns a cobra command for `plugin` subcommands
+func NewPluginCommand(cmd *cobra.Command, dockerCli *command.DockerCli) {
+}