Replace new byte[] full copes with ByteBufUtil.getBytes

We already do it in some places, but we still got plenty of code which does the equivalent of

byte[] packet = new byte[response.readableBytes()];

 response.readBytes(packet);

This can be simplified and also made faster (it will call into unsafe code that avoids zeroe-ing out the array using an intrinsic) by using ByteBufUtil.getBytes in netty