CDK-647: Update examples to use Flume's Log4jAppender and DatasetSink

    * This patch includes configuring the Log4jAppender to gracefully
      handle connection errors. This is useful as it avoids a circular
      dependency between loading the log4j configuration to create the
      dataset and starting Flume after the dataset exists.
    * The README for the logging, logging-webapp, and demo examples have
      been updated accordingly.
    * This patch also includes some fixes needed to work on the CDH5.1
      QuickStart VM. I suspect more of the examples may have issues.
      So I'll file a follow-up JIRA to check them out and to update the
      top-level README to account for changes between the 4.4 and 5.1 VMs.