Adjust unit tests for supporting chain partition with no ab am: e41e464abb am: cdac8f0557 am: 8a3899d76d

Original change: https://android-review.googlesource.com/c/platform/system/tools/mkbootimg/+/2765271

Change-Id: Iaeaf9b99b4411258daadd17ebb107786990004ca
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>