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

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

Change-Id: I2d0b9e02d87a284844487fd8bcaa49a87626820d
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>