LOG4J2-666: AsyncLoggerContextSelector should ensure that different AsyncLoggerContext objects created by web application classloaders have unique names

git-svn-id: https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk@1608149 13f79535-47bb-0310-9956-ffa450edef68
removed underscore prefix from instance variables in async performance test class

git-svn-id: https://svn.apache.org/repos/asf/logging/log4j/log4j2/trunk@1608150 13f79535-47bb-0310-9956-ffa450edef68