Haskell/python compatibility test for networks

This patch contains the HUnit test that checks the compatibility
of Haskell-generated networks with the python code. For that the
generation of test instances of networks was enhanced to meet
the validation steps of the python implementation. Also, so far
networks were generated at two different places in the code; this
is now consolidated.

Signed-off-by: Helga Velroyen <helgav@google.com>
Reviewed-by: Guido Trotter <ultrotter@google.com>