sdk: copy system-qemu.img to system-images.zip

Since init requires system to have partition table
and the original raw system.img does not have it.
system-qemu.img is now created to contain the exact
raw system.img, plus partition table.

When creating the sdk-repo-{host}-system-images.zip
file, using system-qemu.img instead of system.img.

BUG: 64235252

(cherry picked from commit b758d3e8)

Change-Id: I1dee0767a18c52a62ded6eb0b72a06ab93093783