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!)
(cherry picked from commit 34ffa6c44734b99c252e7585bb499089ac8e6a67)