show elasticsearch status !=green `system > indices`

## Expected Behavior
The page `System > indices` should indicate if the Elasticsearch cluster is not in `green` state.

## Context
When debugging and interacting with the customer it is quite normal to look at the `system > indices` page if that returns reasonable results it might be skipped to check the Elasticsearch Cluster health. But it could happen that the cluster is flaky or in yellow state.

## Your Environment

* Graylog Version:3.1

[z#842737]