Network manager refactoring

Part 3.

1. Some cleaning in network manager.
2. A number of network manager tests added.
3. Some refactoring in NetworkConfigurationValidator and NetworkConfigurationVerifyHandlers.
4. Unification of network groups creation and of networks update.
5. Global parameters removed.

Implements: blueprint nailgun-network-manager-refactoring

Change-Id: I688174d4fc9fd3569696e03a8a3067e553d0ac9f
Merge "Network manager refactoring"