In POST:
http://post-office.corp.redhat.com/archives/rhvirt-patches/2013-December/msg00104.html

In previous version like libvirt-0.10.2-29.el6.1,
Libvirt python API will None, and raise a exception:
# python 
Python 2.6.6 (r266:84292, Sep  4 2013, 07:46:00) 
[GCC 4.4.7 20120313 (Red Hat 4.4.7-3)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import libvirt
>>> con=libvirt.open(None)
>>> dom=con.lookupByName('r6')
>>> dom.blockJobInfo('hda', 0)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib64/python2.6/site-packages/libvirt.py", line 1826, in blockJobInfo
    if ret is None: raise libvirtError ('virDomainGetBlockJobInfo() failed', dom=self)
libvirt.libvirtError: virDomainGetBlockJobInfo() failed

This NoneType return is fixed in libvirt-0.10.2-29.el6_5.2:
# python
Python 2.6.6 (r266:84292, Sep  4 2013, 07:46:00) 
[GCC 4.4.7 20120313 (Red Hat 4.4.7-3)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import libvirt
>>> con=libvirt.open(None)
>>> dom=con.lookupByName('r6')
>>> dom.blockJobInfo('hda', 0)
{}

So I change the status to VERIFIED.

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

http://rhn.redhat.com/errata/RHBA-2013-1856.html