iotests: Fix test 128 for password-less sudo

As of 934659c460d46c948cf348822fda1d38556ed9a4, $QEMU_IO is generally no
longer a program name, and therefore "sudo -n $QEMU_IO" will no longer
work.

Fix this by copying the qemu-io invocation function from common.config,
making it use $sudo for invoking $QEMU_IO_PROG, and then use that
function instead of $QEMU_IO.

Reported-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
