Description of problem:
Configure virt-who run at VDSM mode, then run virt-who, it will show "TypeError: __init__() takes exactly 2 arguments (3 given)" when it communication with virtualization backend

Version-Release number of selected component (if applicable):
subscription-manager-1.12.12-1.el6.x86_64
python-rhsm-1.12.5-1.el6.x86_64
virt-who-0.10-6.el6.noarch
katello-headpin-1.4.3.26-1.el6sam_splice.noarch
candlepin-0.9.6.5-1.el6sam.noarch

How reproducible:
Always

Steps to Reproduce:
1. Register system to SAM server.
2. Configure virt-who run at VDSM mode 
VIRTWHO_DEBUG=1
VIRTWHO_BACKGROUND=1
VIRTWHO_INTERVAL=10
VIRTWHO_VDSM=1
3. Restart vdsmd service, then check the vdsmd service run normally.
[root@hp-z220-08 ~]# service vdsmd restart
[root@hp-z220-08 ~]# service vdsmd status
VDS daemon server is running
4. Restart virt-who service
5. Check the virt-who log at /var/log/rhsm/rhsm.log

Actual results:
2014-08-29 14:28:05,618 [INFO]  @virtwho.py:442 - Using virt-who configuration: virt-who
2014-08-29 14:28:05,618 [DEBUG]  @virtwho.py:170 - Starting infinite loop with 10 seconds interval
2014-08-29 14:28:05,710 [ERROR]  @virtwho.py:118 - Error in communication with virtualization backend, trying to recover:
Traceback (most recent call last):
  File "/usr/share/virt-who/virtwho.py", line 111, in _send
    virtualGuests = self._readGuests(config)
  File "/usr/share/virt-who/virtwho.py", line 141, in _readGuests
    virt = Virt.fromConfig(self.logger, config)
  File "/usr/share/virt-who/virt/virt.py", line 63, in fromConfig
    return subsubcls(logger, config)
TypeError: __init__() takes exactly 2 arguments (3 given)
2014-08-29 14:28:05,711 [ERROR]  @virtwho.py:121 - Unable to recover, retry in 10 seconds.

Expected results:
It shouldn't show up any error messages.Virt-who should run normally under the VDSM mode.

Additional info: