Topology refactor / Standalone mode

* Centralizes as much of the topology logic as possible into the `TopoHelper` class (in `ec-common/libraries/topo_helper.rb`)
* Enables standalone topology (actually works)
* Support Analytics node in a much less hacky way
This is where AWS tools look by default for their config, so I followed this same convention and noted it in the README.   However we should revisit this later on, people might want to use environment variables.