Check all node's MACs against MACs of all NICs of nodes

All MACs of node being added/updated are checked against MACs of all NICs of each existing node.
Tests are added.
It's a quick fix. Usage of uuid to determine uniqueness of node will be considered.

Closes-Bug: #1271505

Change-Id: If9e8ac82ff9aa1c8359591821e70d4394a5a24ae
Merge "Check all node's MACs against MACs of all NICs of nodes"