Remove newline from log message (#27425)

It leads to harder-to-parse logs that look like this:

```
  1> [2017-11-16T20:46:21,804][INFO ][o.e.t.r.y.ClientYamlTestClient] Adding header Content-Type
  1>  with value application/json
  1> [2017-11-16T20:46:21,812][INFO ][o.e.t.r.y.ClientYamlTestClient] Adding header Content-Type
  1>  with value application/json
  1> [2017-11-16T20:46:21,820][INFO ][o.e.t.r.y.ClientYamlTestClient] Adding header Content-Type
  1>  with value application/json
  1> [2017-11-16T20:46:21,966][INFO ][o.e.t.r.y.ClientYamlTestClient] Adding header Content-Type
  1>  with value application/json
```

test/framework/src/main/java/org/elasticsearch/test/rest/yaml/ClientYamlTestClient.java

@@ -164,7 +164,7 @@ public ClientYamlTestResponse callApi(String apiName, Map<String, String> params
         Header[] requestHeaders = new Header[headers.size()];
         int index = 0;
         for (Map.Entry<String, String> header : headers.entrySet()) {
-            logger.info("Adding header {}\n with value {}", header.getKey(), header.getValue());
+            logger.info("Adding header {} with value {}", header.getKey(), header.getValue());
             requestHeaders[index++] = new BasicHeader(header.getKey(), header.getValue());
         }