Use status code 429 for circuit breakers

Author: danielmitterdorfer

server/src/main/java/org/elasticsearch/common/breaker/CircuitBreakingException.java

@@ -69,7 +69,7 @@ public long getByteLimit() {
 
     @Override
     public RestStatus status() {
-        return RestStatus.SERVICE_UNAVAILABLE;
+        return RestStatus.TOO_MANY_REQUESTS;
     }
 
     @Override

server/src/test/java/org/elasticsearch/rest/RestControllerTests.java

@@ -279,7 +279,7 @@ public void testDispatchRequestLimitsBytes() {
         int contentLength = BREAKER_LIMIT.bytesAsInt() + 1;
         String content = randomAlphaOfLength((int) Math.round(contentLength / inFlightRequestsBreaker.getOverhead()));
         RestRequest request = testRestRequest("/", content, XContentType.JSON);
-        AssertingChannel channel = new AssertingChannel(request, true, RestStatus.SERVICE_UNAVAILABLE);
+        AssertingChannel channel = new AssertingChannel(request, true, RestStatus.TOO_MANY_REQUESTS);
 
         restController.dispatchRequest(request, channel, new ThreadContext(Settings.EMPTY));