Instrumentation file location should be configurable

To determine where to save the grouperLoader_instrumentation.dat, Grouper looks at whatever FileAppender loggers are defined for log4j, and uses the same directory. If there are no FileAppenders defined, it returns an error "Unable to save an instance id for this instance."

In cases where a configuration does not use a FileAppender (it could be using a ConsoleAppender, for example), there should be a configuration option to specify a filesystem location for the instrumentation data file.