Merge pull request #932 from zalando/ARUHA-1885

ARUHA-1885 Hide unnecessary errors and stack traces while flushing su…

src/main/java/org/zalando/nakadi/service/subscription/state/StreamingState.java

@@ -337,7 +337,7 @@ private void flushData(final EventTypePartition pk, final List<ConsumedEvent> da
 
             batchesSent++;
         } catch (final IOException e) {
-            getLog().error("Failed to write data to output.", e);
+            getLog().warn("Failed to write data to output: {}", e.getMessage());
             shutdownGracefully("Failed to write data to output");
         }
     }