tests: Fix common_config.py issues

tests: Fix common_config.py issues

1) in generate_ips if start_ipaddr does not have a `/` in it
there exists a code path where both mask and step are
null values.  Write a bit of code to ensure this pre-req
is found early and often

2) in verify_rib there exists a code path where static_route
is null when we get to the non static route section.  Change
the code to operate on the advertise_network_dict that
we are iterating over.

Signed-off-by: Donald Sharp <sharpd@nvidia.com>