this the followon to HADOOP-5687 - its not enough to detect bad uris, we need good error messages and a set of tests to make sure everything works as intended.
Starting HDFS with blank configuration fails
setting fs.default.name to an invalid URI format kills init thread in JobTracker
NPE when the namenode comes up but the filesystem is set to file://
Hadoop NameNode throws NPE if fs.default.name is the default value