Make network policy (ACL/PG/AS) configuration more generic.

[dceara]

We currently encode all the logic for simulating network policies, i.e., ACL, Port_Group, Address_Set in python scenarios. It might be better and more flexible to have a generic mechanism to specify such configuration externally. One option is described here:

"For the network policy related port-groups and ACLs, it seems to me better to be created as configuration (in JSON format) instead of adding to the code implementation. In the code we can add the support to apply whatever port-groups and ACLs that is configured, so that it is easier to test scalability of different port-group/ACL configurations."

CC: @hzhou8
CC: @LorenzoBianconi