Ticket 47910 - logconv.pl - check that the end time is greater than the start time
    
    Bug Description:  There is no check if the end time is greater than the start time.
                      This leads to an empty report being generated, when an error
                      should be returned instead.
    
    Fix Description:  If start and end time are used, validate that the end time is
                      greater than the start time.
    
                      Also, improved an error message when the tool options are not
                      correctly used.
    
    https://fedorahosted.org/389/ticket/47910
    
    Reviewed by: nhosoi(Thanks!)