aarch64: Use a smaller test file for test-cancellation-upload-daemoncancels.sh

This test worked by uploading a 100MB file into a 100MB container and
seeing the inevitable crash.  Unfortunately virtio-mmio (used on
aarch64) is quite slow.  Since this test is not testing the speed of
virtio-mmio, use a smaller test file so the test finishes in a
reasonable time.