Qemu: Use all CPU cores am: 7a490b995a am: e33b0062e9

Original change: https://android-review.googlesource.com/c/platform/art/+/2984614

Change-Id: I95bf1e0eee56460793ce01c90366c4b1f4ffddb7
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>