Description of problem:

virt-v2v can not convert guest which disk use the block device 


Version-Release number of selected component (if applicable):

virt-v2v-0.7.1-4.el5
libvirt-0.8.2-20.el5
libguestfs-1.2.7-1.el5.15
hivex-1.2.2-1.el5.1
package augeas is not installed
virtio-win-1.0.1-3.52454.el5


How reproducible:
100%

Steps to Reproduce:
1.create a new pool in a usb device 

<pool type='disk'>
  <name>sdb</name>
  <source>
    <device path='/dev/sdb'>
    </device>
    <format type='dos'/>
  </source>
  <target>
    <path>/dev</path>
    <permissions>
      <mode>0700</mode>
      <owner>0</owner>
      <group>0</group>
    </permissions>
  </target>
</pool>

2.create a volume and setup a guest 

3.  convert the guest 
virt-v2v -ic qemu+ssh://10.66.11.181/system -os v2v5 test
root.11.181's password: 
virt-v2v: Failed to create storage volume: libvirt error code: 27, message: XML description for unknown volume format type none is not well formed or invalid
  
Actual results:
error exit

Expected results:
convert successfully 


Additional info:
can not convert to rhevm too :
virt-v2v: RHEV cannot handle volumes of format none