Save topology needs ES to be reachable on startup

[tsg]

The Elastitcsearch output generally doesn't require ES to be reachable when Packetbeat starts, but the save topology code actually does and exists if ES is not reachable on 3 retries. While this is somehow convenient for detecting configuration errors it's problem when ES and Packetbeat are started in parallel and Packetbeat comes up first.

We should also look into moving the topology code out of libbeat and into Packetbeat, as it is specific to it.