Refactored RouteComparison.comparison_check to search 'null tag' in hop
Refactored RouteComparison.comparison_check to search 'null tag' in hop

Issue: Previous commit changed Traceroute.__generate_domain_list
       to properly present unknown/'*' hops as 'None' to
       'null tag:<destination_ip>_<traceroute_hop_index>'. Thus
       RouteComparison.comparison_check was still looking for 'None'
       equivalent values (None, False, 0, etc) when it should have been
       searching for 'null tag:' values.

Solution: Changed the if statement within the list comprehension found
          in RouteComparison.comparison_check to check for 'null tag:'
          values.

spgreen/psTrace