Configuring custom logger for MDCSiftingAppender on Fuse 7

Issue

Many Fuse 6.x customers use the log4j appender class org.apache.log4j.sift.MDCSiftingAppender to specify per-bundle logging, or logging that is configured in some way using application-defined keys.
For Fuse 7 you can specify a bundle custom logger for your code for achieving this. Or there is another solution, Fuse 7 on Karaf: log4j2 does not support MDCSiftingAppender if you prefer using the root logger, and not specifying the logger in your code, however, the other solution generate a file for each Fuse bundle, and this one generates only one file for the bundle with the code changes