move some io related utils to pkg/ioutils

Docker-DCO-1.1-Signed-off-by: Cristian Staretu <cristian.staretu@gmail.com> (github: unclejack)

ioutils/writers.go

@@ -0,0 +1,23 @@
+package ioutils
+
+import "io"
+
+type NopWriter struct{}
+
+func (*NopWriter) Write(buf []byte) (int, error) {
+	return len(buf), nil
+}
+
+type nopWriteCloser struct {
+	io.Writer
+}
+
+func (w *nopWriteCloser) Close() error { return nil }
+
+func NopWriteCloser(w io.Writer) io.WriteCloser {
+	return &nopWriteCloser{w}
+}
+
+type NopFlusher struct{}
+
+func (f *NopFlusher) Flush() {}