test.tmpdir contains some string as "tmpXMoLDh_virt.libvirt.qcow2.virtio_blk.smp2.virtio_net.Fedora.18.x86_64.q35.virsh.blockcopy.positive_test". It seems that qemu command 'drive-mirror' can not parse "." in path. 
I got an error here 
```
error: internal error unable to execute QEMU command 'drive-mirror': /home/yds/github-autotest/github-autotest/client/tmp/tmp/tmpXMoLDh_virt.libvirt.qcow2.virtio_blk.smp2.virtio_net.Fedora.18.x86_64.q35.virsh.blockcopy.positive_test.no_option/2014-01-13-16.49.04.img: error while creating qcow2: Permission denied
```

I suggest use data_dir.get_tmp_dir() to replace test.tmpdir here, and it works well on my F19.