Merge "fs_mgr: Add OverlayMountPoints() to get the list of overlayfs backing storage" am: ec1b09fca9 am: 9a2bf07d51 am: cd369c3cec

Original change: https://android-review.googlesource.com/c/platform/system/core/+/1585166

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: I913a27ccaef107c67bb1e8083e4715f384269043