Use sets to calculate added/original/removed ips

Use sets to calculate added/original/removed ips

Original algorithm to calculate added/removed ips had O(n^2) complexity.
Using sets achieves O(n) for average case.
After refactoring input is no longer affected,
updated tests to reflect that.
However, dataset is too small to get any significant performance
improvement.

Using sets requires additional preparation and post operations:
- converting 'original_ips' and 'new_ips' to sets from ip_addresses
- building map(dict) for storing reference from ip_address to 'ips'
  element
- converting calculated add/orignal/remove sets back to list of dicts
  using map (dict of references).

Partially-Implements: blueprint neutron-ipam

Change-Id: Iecddc406f7b91cfdfb976882504113734e19b565