Add PReadAll/PWriteAll for filedescriptor ptr am: c3c0a3ab46 am: f8decd3431 am: 1d8709bc12

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/1493018

Change-Id: I44204cb13d3aaecccdb17218c6b01c7f15a91c13