CDK-668: Update maven plugin to setup DefaultConfiguration.

Previously, properties set in the plugin's configuration were local and
the getDatasetRepository method had to use repository builders to use
the correct file system. This updates the method to create repository
URIs instead and changes the getConf method to update the default
Configuration.
For repository URIs, this is consistent. All of file, webhdfs, hdfs, and hive (external) all use the path for the repository root. The dataset URIs change a bit more, but I think that we are as consistent as we can be after CDK-633.