Description of problem:
occasionally when running with oz 0.7.0, oz fails to generate an image and instead prints the following error:
Libvirt Block Stats Failed:
 code is 55
 domain is 10
 message is Requested operation is not valid: domain is not running
 level is 2
 str1 is Requested operation is not valid: %s
 str2 is domain is not running
 str3 is None
 int1 is -1
 int2 is -1
Cleaning up guest named U10-x86_64-jeos
Cleaning up after install
Traceback (most recent call last):
  File "/usr/bin/oz-install", line 152, in <module>
    libvirt_xml = guest.install(timeout, force_download)
  File "/usr/lib/python2.7/site-packages/oz/Ubuntu.py", line 144, in install
    return self._do_install(timeout, force, 0)
  File "/usr/lib/python2.7/site-packages/oz/Guest.py", line 1413, in _do_install
    self._wait_for_install_finish(dom, timeout)
  File "/usr/lib/python2.7/site-packages/oz/Guest.py", line 505, in _wait_for_install_finish
    rd_req, rd_bytes, wr_req, wr_bytes, errs = libvirt_dom.blockStats(dev)
  File "/usr/lib64/python2.7/site-packages/libvirt.py", line 1394, in blockStats
    if ret is None: raise libvirtError ('virDomainBlockStats() failed', dom=self)
libvirt.libvirtError: Requested operation is not valid: domain is not running


Version-Release number of selected component (if applicable):
I am using master although this problem has existed since oz 0.4 or so.

How reproducible:
10-15%

Steps to Reproduce:
1. oz install an image
2. sometimes it fails
3.
  
Actual results:
fails

Expected results:
shouldn't fail

Additional info:
running f16 now.  In f15, libvirt actually segfaulted.  This may still be happening - it is hard to tell with systemd.