With 8e438a44, we started signing QA APKs with a more recent version of
apksigner, but it wasn't enough, because the starting .apk needs to be already aligned.
I missed that step, which this MR adds.
Also, it removes a RBM variable that I had initially added to add the build tools to
$PATH change has been added to
android-toolchain, in the final revision of 8e438a44).