Move engine-api client package

This moves the engine-api client package to `/docker/docker/client`.

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>

client/checkpoint_create.go

@@ -0,0 +1,13 @@
+package client
+
+import (
+	"github.com/docker/docker/api/types"
+	"golang.org/x/net/context"
+)
+
+// CheckpointCreate creates a checkpoint from the given container with the given name
+func (cli *Client) CheckpointCreate(ctx context.Context, container string, options types.CheckpointCreateOptions) error {
+	resp, err := cli.post(ctx, "/containers/"+container+"/checkpoints", nil, options, nil)
+	ensureReaderClosed(resp)
+	return err
+}