@Override
    public String getStagingDirectory(String key) {
      return prefix + key;
    }
Trivial implementation of StagingDirectoryProvider which takes a temporary directory
and creates directories inside that for each key. Note that this is intended as a
trivial implementation, and if any further "advanced" behaviour is desired,
it is better that the user roll their own.

@param base temp directory inside which other tmp dirs are created
@param separator path separator. Usually should be "/"
hcatalog/webhcat/java-client/src/main/java/org/apache/hive/hcatalog/api/repl/StagingDirectoryProvider.java