Fixup InternalEngineTests

Author: prdoyle

server/src/test/java/org/elasticsearch/index/engine/InternalEngineTests.java

@@ -2538,7 +2538,7 @@ public void testIndexWriterInfoStream() throws IllegalAccessException, IOExcepti
         Level savedLevel = theLogger.getLevel();
         Loggers.addAppender(theLogger, mockAppender);
         Loggers.setLevel(theLogger, Level.DEBUG);
-        theLogger = LogManager.getRootLogger();
+        theLogger = LogManager.getLogger("org.elasticsearch.index");
 
         try {
             // First, with DEBUG, which should NOT log IndexWriter output: