Merge "fs_mgr: Split fs_mgr_overlayfs into two separate files." into main am: 3d0a332ff5 am: f7a0081b99 am: d498683a72

Original change: https://android-review.googlesource.com/c/platform/system/core/+/2656899

Change-Id: Ia437420bed5951154fb4c2220580ebdc24d6fac8
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>