Summary: folly AsyncPipeReader takes a callback of type AsyncReader::ReadCallback. Now AsyncReader::ReadCallback class supports IOBuf as a buffer for transfer read bytes. Need to extend AsyncPipeReader class to support IOBuf as well

Reviewed By: yfeldblum

Differential Revision: D3650893

fbshipit-source-id: e2142341c8b8b0b2ef248c1f13a8caba9d50ba67