Feature: import goodies from bt-hcc repo

Adds stuff to core brooklyn, from bt-hcc repo:
1. Entities.attributeSupplier and other related helper methods
2. SameServerEntity (which creates a machine and then passes that machine to each of its child entities)
3. Zabbix support (but in sanbox, because code assumes agent is pre-installed currently; also note I added ZabbixFeed.Builder.uniqueHostnameGenerator so that bt-hcc can supply its custom logic for this).

We still need to move MySql cluster from bt-hcc into core brooklyn. That will be a different pull request.