Updates repack_gki.py for ABI XML rename and lack of 5.15 boot.img. am: 08514c337d am: 7d0040de74 am: 5b5f163008 am: 17389ce6d4

Original change: https://android-review.googlesource.com/c/platform/tools/treble/+/1909611

Change-Id: I1f7ed5e4bb516cf588bceb4004344c2cd0b1be90