Expose this option at `merge_builds.py` so that this script
can also resolve the conflict AVB rollback index location
while building the vbmeta image.
Bug: 289368551
Test: TreeHugger
Change-Id: I404160ff5d7591cb6a81ed2d2267de1b0e6ac65f
This will be used in the following change to split
merge_target_files into a collection of smaller
more-focused scripts.
Bug: 221858722
Test: m otatools; Use to create merged builds
Change-Id: Ie01dac81c5f9f28f1e0fe037259eabd2478e60b6