qemu-iotests: disable default qemu devices for cross-platform compatibility

qemu-iotests: disable default qemu devices for cross-platform compatibility

This patch fixes an io test suite issue that was introduced with the
commit c88930a6866e74953e931ae749781e98e486e5c8 'qemu-char: Permit only
a single "stdio" character device'. The option supresses the creation of
default devices such as the floopy and cdrom. Output files for test case
067, 071, 081 and 087 need to be updated to accommodate this change.
Use virtio-blk instead of virtio-blk-pci as the device driver for test
case 067. For virtio-blk-pci is the same with virtio-blk as device
driver but other platform such as s390 may not recognize the virtio-blk-pci.

The default devices differ across machines. As the qemu output often
contains these devices (or events for them, like opening a CD tray on
reset), the reference output currently is rather machine-specific.

All existing qemu tests explicitly configure the devices they're working
with, so just pass -nodefaults to qemu by default to disable the default
devices. Update the reference outputs accordingly.

Reviewed-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Michael Mueller <mimu@linux.vnet.ibm.com>
Reviewed-by: Sascha Silbe <silbe@linux.vnet.ibm.com>
Signed-off-by: Xiao Guang Chen <chenxg@linux.vnet.ibm.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>