Fix crash on LiveCD if network is configured before installing (#1002373)
    
    On LiveCD if network is configured before starting installation, the connection
    is saved into ifcfg file (ifcfg-Wired_connection_1) and
    
    1) instead of ignoring it, the file was updated with our id and onboot value
    in dumpMissingDefaultIfcfgs
    
    in (frequent) case of only one wired device
    
    2) the ifcfg file for the device was expected to be named using device name
    eg ifcfg-ens3 in setNetworkOnbootDefault => traceback
    
    This is a moderate fix for Alpha.
    I am going to come with bigger patch cleaning up ifcfg files handling.