When daemon is killed right in the middle of probing a qemu binary for
its capabilities, the qemu process is left running.  Next time the
daemon is starting, it cannot start the probing qemu process because the
one that's already running does have the pidfile flock()'d.
Reported-by: NWang Yufei <james.wangyufei@huawei.com>
Signed-off-by: NMartin Kletzander <mkletzan@redhat.com>