fenced: fix log file mode
    
    Remove umask(0) which caused liblogthread's fopen to
    create fenced.log with mode 666.
    
    Check if existing fenced.log has mode 666 and if so,
    chmod to 644.
    
    bz 845341
    
    Signed-off-by: David Teigland <teigland@redhat.com>