Merge "Allow BOARD_BUILD_SYSTEM_ROOT_IMAGE override by command line flag." am: c32d31d4fa

Original change: https://android-review.googlesource.com/c/device/generic/common/+/2039603

Change-Id: I209eb5009d5af0bb4530f8dfecd59a497c6a102b
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>