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.
The NN is configured in the core-site.xml file under src/main/resources of the demo-crunch, demo-logging-webapp, and demo-oozie modules. It's also configured in the pom.xml of the parent demo module and the demo-oozie module.

The problem is that if you leave those as localhost, which is what they were before these changes, then various commands fail. I forgot to record the exception, but it was one I've seen before where you can't access the metadata because the NN's URI doesn't match what gets written.