Polish recent changes to Log4jWebConfigurer

Reordered inline comments so that they now apply to current
state of the code.

Added logger entry in testlog4j.properties to avoid console
warning.

Issue: SPR-9417

spring-web/src/test/resources/org/springframework/web/util/testlog4j.properties

@@ -1,2 +1,5 @@
 log4j.rootCategory=DEBUG, mock
-log4j.appender.mock=org.springframework.web.util.MockLog4jAppender
+
+log4j.appender.mock=org.springframework.web.util.MockLog4jAppender
+
+log4j.logger.org.springframework.mock.web=WARN