Description of problem:
Discovered when testing/debugging the issue reported in bug 674356, if the dnsmasq server fails to start it happens with an incorrect failure message.

Version-Release number of selected component (if applicable):
0.8.4

How reproducible:
100%

Steps to Reproduce:
See steps in bug 674356
  
Actual results:
In virt-manager one gets the following error:

Error creating virtual network: internal error '/sbin/iptables --table mangle --delete POSTROUTING --out-interface virbr2 --protocol udp --destination-port 68 --jump CHECKSUM --checksum-fill' exited with non-zero status 2 and signal 0: iptables v1.4.4: unknown option `--checksum-fill'
Try `iptables -h' or 'iptables --help' for more information.

Traceback (most recent call last):
  File "/usr/share/virt-manager/virtManager/createnet.py", line 349, in finish
    self.conn.create_network(xml)
  File "/usr/share/virt-manager/virtManager/connection.py", line 755, in create_network
    net.create()
  File "/usr/lib/python2.6/dist-packages/libvirt.py", line 866, in create
    if ret == -1: raise libvirtError ('virNetworkCreate() failed', net=self)
libvirtError: internal error '/sbin/iptables --table mangle --delete POSTROUTING --out-interface virbr2 --protocol udp --destination-port 68 --jump CHECKSUM --checksum-fill' exited with non-zero status 2 and signal 0: iptables v1.4.4: unknown option `--checksum-fill'
Try `iptables -h' or 'iptables --help' for more information.

Expected results:
Should see a failure message logged by libvirtd reflecting the failure to start dnsmasq.

The reported error is of course a red herring in that it's a non-fatal error.  What is fatal though is the failure to start dnsmasq and that goes completely unreported.