Add a simple watchdog for logstash-indexer service

The logstash-indexer services sometimes fall out of the elasticsearch
cluster when it is under heavy load and unable to respond to pings.
Logstash doesn't do anything to reconnect :( so restart the service if a
node detects that it has fallen out of the cluster.

Upstream bug submitted at https://logstash.jira.com/browse/LOGSTASH-1951

Change-Id: I2e7767c5fe20cff279366fec2ddadd7710dbb4a9
Merge "Add a simple watchdog for logstash-indexer service"