vendor new client and api

Signed-off-by: Riyaz Faizullabhoy <riyaz.faizullabhoy@docker.com>

vendor/github.com/docker/docker/client/plugin_set.go

@@ -0,0 +1,12 @@
+package client
+
+import (
+	"golang.org/x/net/context"
+)
+
+// PluginSet modifies settings for an existing plugin
+func (cli *Client) PluginSet(ctx context.Context, name string, args []string) error {
+	resp, err := cli.post(ctx, "/plugins/"+name+"/set", nil, args, nil)
+	ensureReaderClosed(resp)
+	return err
+}