change logging level of testTimeoutSendExceptionWithDelayedResponse to TRACE
Plugin Manager: add silent mode.
Now with have proper exit codes for elasticsearch plugin manager (see #3463), we can add a silent mode to plugin manager.

```sh
bin/plugin --install karmi/elasticsearch-paramedic --silent
```

Closes #3628.
Added clear scroll api.

The clear scroll api allows clear all resources associated with a `scroll_id` by deleting the `scroll_id` and its associated SearchContext.

Closes #3657
Rewrote SuggestResponse#toString method

It only prints out json now (as the SearchResponse does)
Added missing startObject & endObject (was causing JsonGenerationException)

Closes #3661