Merge "Add a function pointer to get active boot slot" am: c4b24df2ef am: 8281ca965f am: afd797f823

Original change: https://android-review.googlesource.com/c/platform/hardware/libhardware/+/1514949

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: I3ee3f1b00302b9f7719bdbefa3700356cc8168ae