Description of problem:
virsh update-device can't update an xml file as to an inactive domain. The following error messages appear: 
virsh update-device <domian-id> <xml-file>
error: Failed to update device from <xml-file>
error: Requested operation is not valid: cannot attach device on inactive domain

The operation works without error with active domain.

Version-Release number of selected component (if applicable):
Red Hat Enterprise Linux Version Number: 6.0
Kernel Version: kernel-2.6.32-71.el6.i686
Related Package Version: libvirt-client-0.8.1-27.el6.i686 

How reproducible:
Always

Steps to Reproduce:
1. Make sure the guest is stopped. 
2. Attach a DVD image to the kvm guest OS by virt-manager.
3. Create an xml file to detach the DVD image. E.g: 
# less /tmp/foo.xml
<disk type='file' device='cdrom'>
<driver name='qemu' type='raw'/>
<target dev='hdc' bus='ide'/>
<readonly/>
<address type='drive' controller='0' bus='1' unit='0'/>
</disk>
4. Update an xml file of the kvm guest. 
# virsh update-device <domain-id> /tmp/foo.xml  


Actual results:
virsh update-device can't update an xml file because the domain is inactive. 

Expected results:
virsh update-device should be able to update the xml file. 


Additional info: