It has been found that the libvirt network interface will be wedged somehow, if the oz command is run several times. A working network is needed by oz in order to update the virtual machine with cloud-init and several other package updates. A solution to this problem can be to destroy and recreate the network. More details on this issue can be seen at (813853) (https://bugzilla.redhat.com/show_bug.cgi?id=813853):
sudo virsh net-destroy default sudo virsh net-start default
If the preceding solution does not solve the issue, then one reason could be one or more zombie dnsmasq processes.
During oz customization, the virsh console command can be used to log into the virtual machine using credentials root/ozrootpw.