block: Use QEMU_CLOCK_VIRTUAL for the accounting code in qtest mode

block: Use QEMU_CLOCK_VIRTUAL for the accounting code in qtest mode

This patch switches to QEMU_CLOCK_VIRTUAL for the accounting code in
qtest mode, and makes the latency of the operation constant. This way we
can perform tests on the accounting code with reproducible results.

Signed-off-by: Alberto Garcia <berto@igalia.com>
Message-id: 35ed0501450fa572684e9b5e92c361ab6cce565b.1446044838.git.berto@igalia.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>