Support certifying the boot.img in a boot-img.tar.gz am: 90a8372549 am: 3d88178cf6 am: b970cf0272 am: da6c21fa55

Original change: https://android-review.googlesource.com/c/platform/system/tools/mkbootimg/+/2109068

Change-Id: Ic7d357c177f16f36f236817f8924779292d5c431
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>