Adjust unit tests for supporting chain partition with no ab am: e41e464abb am: cdac8f0557 am: 8a3899d76d am: 773e4ebd8f

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

Change-Id: I784c2e6c8763053f84a3402d14e30110f56f5114
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>