Description of problem:
When the guest images already exist in local pool,virt-v2v prints waring:WARNING:/boot/grub/device.map references unknown device /dev/vda

Version-Release number of selected component (if applicable):
virt-v2v-0.8.6-1.el6.x86_64
libvirt-0.9.10-1.el6.x86_64
libguestfs-1.16.5-1.el6.x86_64

How reproducible:
always

Steps to Reproduce:
1.Use virt-v2v to convert a guest.
# virt-v2v  -ic qemu+ssh://10.66.72.122/system -os default -b rhevm kvm-rhel6.2-x86_64
The authenticity of host '10.66.72.122 (10.66.72.122)' can't be established.
RSA key fingerprint is 0e:e6:24:0e:16:b3:10:73:44:e8:7b:f2:fd:39:6f:66.
Are you sure you want to continue connecting (yes/no)? yes
root.72.122's password:
root.72.122's password:
kvm-rhel6.1-x86_64.img: 100% [====================================================================================]D 0h03m55s
virt-v2v: WARNING: The connected hypervisor does not support feature pae.
virt-v2v: kvm-rhel6.2-x86_64 configured with virtio drivers.

2.Undefine the converted guest:
# virsh list --all
 Id    Name                           State
----------------------------------------------------
 -     kvm-rhel6.2-x86_64             shut off

# virsh undefine kvm-rhel6.2-x86_64
Domain kvm-rhel6.2-x86_64 has been undefined

3.Use virt-v2v to convert the guest again:
# virt-v2v  -ic qemu+ssh://10.66.72.122/system -os default -b rhevm kvm-rhel6.2-x86_64
root.72.122's password:
virt-v2v: WARNING: Storage volume kvm-rhel6.1-x86_64.img already exists on the target. NOT copying it again. Delete the volume and retry to copy again.
virt-v2v: WARNING: /boot/grub/device.map references unknown device /dev/vda. This entry must be manually fixed after conversion.
virt-v2v: WARNING: The connected hypervisor does not support feature pae.
virt-v2v: kvm-rhel6.2-x86_64 configured with virtio drivers.



Actual results:
There is warning:virt-v2v: WARNING: /boot/grub/device.map references unknown device /dev/vda. This entry must be manually fixed after conversion.

Expected results:
There is should no warning as actual results.


Additional info:
1.When tested with virt-v2v-0.8.3-5.el6.x86_64,there is no such warning.
# virt-v2v  -ic qemu+ssh://10.66.72.122/system -os default -b rhevm kvm-rhel6.2-x86_64
root.72.122's password:
virt-v2v: WARNING: Storage volume kvm-rhel6.1-x86_64.img already exists on the target. NOT copying it again. Delete the volume and retry to copy again.
virt-v2v: WARNING: The connected hypervisor does not support feature pae.
virt-v2v: kvm-rhel6.2-x86_64 configured with virtio drivers.