Rewriting Riemann output plugin (#1900)

* rename to riemann_legacy

Signed-off-by: Fabio Berchtold <fabio.berchtold@swisscom.com>

* initial draft for Riemann output plugin rewrite

Signed-off-by: Fabio Berchtold <fabio.berchtold@swisscom.com>

* add unit tests

Signed-off-by: Fabio Berchtold <fabio.berchtold@swisscom.com>

* add option to send string metrics as states

Signed-off-by: Fabio Berchtold <fabio.berchtold@swisscom.com>

* add integration tests

Signed-off-by: Fabio Berchtold <fabio.berchtold@swisscom.com>

* add plugin README.md

Signed-off-by: Fabio Berchtold <fabio.berchtold@swisscom.com>

* bump riemann library

* clarify settings description

Signed-off-by: Fabio Berchtold <fabio.berchtold@swisscom.com>

* update Readme.md with updated description

Signed-off-by: Fabio Berchtold <fabio.berchtold@swisscom.com>

* add Riemann event examples

Signed-off-by: Fabio Berchtold <fabio.berchtold@swisscom.com>

* use full URL for Riemann server address

Signed-off-by: Fabio Berchtold <fabio.berchtold@swisscom.com>

closes #1878

Makefile

@@ -58,7 +58,7 @@ docker-run:
 	docker run --name redis -p "6379:6379" -d redis
 	docker run --name nsq -p "4150:4150" -d nsqio/nsq /nsqd
 	docker run --name mqtt -p "1883:1883" -d ncarlier/mqtt
-	docker run --name riemann -p "5555:5555" -d blalor/riemann
+	docker run --name riemann -p "5555:5555" -d stealthly/docker-riemann
 	docker run --name nats -p "4222:4222" -d nats
 
 # Run docker containers necessary for CircleCI unit tests
@@ -71,7 +71,7 @@ docker-run-circle:
 		-d spotify/kafka
 	docker run --name nsq -p "4150:4150" -d nsqio/nsq /nsqd
 	docker run --name mqtt -p "1883:1883" -d ncarlier/mqtt
-	docker run --name riemann -p "5555:5555" -d blalor/riemann
+	docker run --name riemann -p "5555:5555" -d stealthly/docker-riemann
 	docker run --name nats -p "4222:4222" -d nats
 
 # Kill all docker containers, ignore errors