Unconditionally clear the process handle when nm-c-e exits (#1132645)
    
    GLib.child_watch_add has called waitpid on the process at this point, so
    trying to do anything else with the Popen object afterwards will result
    in bad times.
    
    Also combine the two exit handlers because they do pretty much the same
    things, and unconditionally log the nm-c-e exit status.