Description of problem:
virt-v2v: warning: /files/boot/grub/device.map/hd0 references unknown  device "sda"  when convert a guest with ide bus

Version-Release number of selected component (if applicable):
libguestfs-1.27.62-1.1.el7.x86_64
virt-v2v-1.27.62-1.1.el7.x86_64
libvirt-1.2.8-5.el7.x86_64

How reproducible:
100%

Steps to Reproduce:
1. Prepare a guest with ide bus:
# virsh dumpxml rhel6.5-2 |grep -A5 disk

    <disk type='file' device='disk'>
      <driver name='qemu' type='qcow2'/>
      <source file='/var/lib/libvirt/images/rhel6.5-2.qcow2'/>
      <target dev='hda' bus='ide'/>
      <address type='drive' controller='0' bus='0' target='0' unit='0'/>
    </disk>

Before conversion,check /boot/grub/device.map:
# cat /boot/grub/device.map
# this device map was generated by anaconda
(hd0)     /dev/sda

2. Use virt-v2v convert guest "rhel6.5-2" to rhevm server, warning shows like:
virt-v2v: warning: /files/boot/grub/device.map/hd0 references unknown
device "sda".  You may have to fix this entry manually after conversion.
virt-v2v: warning: /files/etc/sysconfig/grub/boot references unknown device
"sda".  You may have to fix this entry manually after conversion.

# virt-v2v -o rhev -os 10.66.90.115:/vol/v2v_auto/auto_export rhel6.5-2  --network rhevm -on rhel6-juzhou2  -of qcow2
[   0.0] Opening the source -i libvirt rhel6.5-2
[   0.0] Creating an overlay to protect the source from being modified
[   0.0] Opening the overlay
[   3.0] Initializing the target -o rhev -os 10.66.90.115:/vol/v2v_auto/auto_export
virt-v2v: warning: cannot write files to the NFS server as 36:36, even
though we appear to be running as root. This probably means the NFS client
or idmapd is not configured properly.

You will have to chown the files that virt-v2v creates after the run,
otherwise RHEV-M will not be able to import the VM.
[   3.0] Inspecting the overlay
[   6.0] Checking for sufficient free disk space in the guest
[   6.0] Estimating space required on target for each disk
[   6.0] Converting Red Hat Enterprise Linux Server release 6.6 (Santiago) to run on KVM
virt-v2v: warning: The display driver was updated to 'qxl', but X11 does
not seem to be installed in the guest.  X may not function correctly.
virt-v2v: warning: /files/boot/grub/device.map/hd0 references unknown
device "sda".  You may have to fix this entry manually after conversion.
virt-v2v: warning: /files/etc/sysconfig/grub/boot references unknown device
"sda".  You may have to fix this entry manually after conversion.
This guest has virtio drivers installed.
[  28.0] Mapping filesystem data to avoid copying unused and blank areas
[  30.0] Closing the overlay
[  30.0] Copying disk 1/1 to /tmp/v2v.L9G5gT/46adae8a-63c1-40f8-b25a-f02deb1a5160/images/89e1fa86-a7c7-4bc4-be38-831a98d3253e/59be4437-c5ff-43d8-a76f-98b87d69778c (qcow2)
    (100.00/100%)
[  46.0] Creating output metadata
[  46.0] Finishing off

3. Login rhevm server and import guest then start guest check:
# cat /boot/grub/device.map
# this device map was generated by anaconda
(hd0)     /dev/sda

Actual results:
As described.

Expected results:
No such warning shows in Step2.

Additional info:
Since i used a guest without x-window, so the following warning message is accepted i think:
virt-v2v: warning: The display driver was updated to 'qxl', but X11 does
not seem to be installed in the guest.  X may not function correctly.