copy using bytes pools

Vendor and use docker/pkg/pools.
pools are used to lower the number of memory allocations and reuse buffers when
processing large streams operations..

The use of pools.Copy avoids io.Copy's internal buffer allocation.
This commit replaces io.Copy with pools.Copy to avoid the allocation of
buffers in io.Copy.

Signed-off-by: Antonio Murdaca <runcom@redhat.com>

server/container_attach.go

@@ -10,6 +10,7 @@ import (
 	"syscall"
 
 	"github.com/Sirupsen/logrus"
+	"github.com/docker/docker/pkg/pools"
 	"github.com/kubernetes-incubator/cri-o/oci"
 	"github.com/kubernetes-incubator/cri-o/utils"
 	"golang.org/x/net/context"
@@ -108,7 +109,7 @@ func redirectResponseToOutputStream(tty bool, outputStream, errorStream io.Write
 	}
 	var err error
 	if tty {
-		_, err = io.Copy(outputStream, conn)
+		_, err = pools.Copy(outputStream, conn)
 	} else {
 		// TODO
 	}