Pure GSI build targets has no vendor partition, such as
aosp_$arch_ab and gsi_$arch. The system properties defined by
PRODUCT_PROPERTY_OVERRIDES will be in /system/build.prop.
The patch defined a fake BOARD_VENDORIMAGE_FILE_SYSTEM_TYPE to
let these system properties flow to vendor and won't pollute the
system.img.
The bug also move some properties to /product/build.prop.
Bug: 135508595
Bug: 131162245
Bug: 134781120
Test: check the /system/build.prop do not have "ro.carrier=unknown"
Test: adb remount on GSI Q on P
Change-Id: Ib200d66cf98fea572c26338e058bce29eb5e0cd7
79e0d25c33