Create /etc/sysconfig/network if it doesn't exist
    
    When the --hostname option is given to ipa-client-install, we
    write HOSTNAME to /etc/sysconfig/network. When that file didn't exist,
    the installer crashed.
    
    Create the file if it doesn't exist and we need to write to it.
    
    https://fedorahosted.org/freeipa/ticket/2840