cherry-picked several fixes (for crashes)
    
    - dispatcher: fix crash on exit while logging from signal handler (rh #1017884)
    - core: workaround crash when connecting to wifi (rh #1025371)
    - ethernet: don't crash if device doesn't have a MAC address (rh #1029053)
    - libnm-glib: fix crash by taking additional ref in result_cb() (rh #1030403)
    - ifcfg-rh: fix ignoring updates that don't change anything