Fix windows build for client

Move io copy logic from ctr utils to io_windows.go.
Fix compilation errors on Windows.

Signed-off-by: Derek McGowan <derek@mcgstyle.net>

io_unix.go

@@ -0,0 +1,71 @@
+// +build !windows
+
+package containerd
+
+import (
+	"context"
+	"io"
+	"sync"
+	"syscall"
+
+	"github.com/containerd/fifo"
+)
+
+func copyIO(fifos *fifoSet, ioset *ioSet, tty bool) (closer io.Closer, err error) {
+	var (
+		f   io.ReadWriteCloser
+		ctx = context.Background()
+		wg  = &sync.WaitGroup{}
+	)
+
+	if f, err = fifo.OpenFifo(ctx, fifos.in, syscall.O_WRONLY|syscall.O_CREAT|syscall.O_NONBLOCK, 0700); err != nil {
+		return nil, err
+	}
+	defer func(c io.Closer) {
+		if err != nil {
+			c.Close()
+		}
+	}(f)
+	go func(w io.WriteCloser) {
+		io.Copy(w, ioset.in)
+		w.Close()
+	}(f)
+
+	if f, err = fifo.OpenFifo(ctx, fifos.out, syscall.O_RDONLY|syscall.O_CREAT|syscall.O_NONBLOCK, 0700); err != nil {
+		return nil, err
+	}
+	defer func(c io.Closer) {
+		if err != nil {
+			c.Close()
+		}
+	}(f)
+	wg.Add(1)
+	go func(r io.ReadCloser) {
+		io.Copy(ioset.out, r)
+		r.Close()
+		wg.Done()
+	}(f)
+
+	if f, err = fifo.OpenFifo(ctx, fifos.err, syscall.O_RDONLY|syscall.O_CREAT|syscall.O_NONBLOCK, 0700); err != nil {
+		return nil, err
+	}
+	defer func(c io.Closer) {
+		if err != nil {
+			c.Close()
+		}
+	}(f)
+
+	if !tty {
+		wg.Add(1)
+		go func(r io.ReadCloser) {
+			io.Copy(ioset.err, r)
+			r.Close()
+			wg.Done()
+		}(f)
+	}
+
+	return &wgCloser{
+		wg:  wg,
+		dir: fifos.dir,
+	}, nil
+}