Treats empty package.__path__ like it's missing
Merge pull request #453 from Houzz/ignore_empty_package_path

Treats empty package.__path__ like it's missing
hdfs: Use logger rather than print statements

I tested this by running the following on a hdfs-configured machine:

    import luigi.hdfs
    import luigi.interface

    luigi.interface.setup_interface_logging()

    pipe = luigi.hdfs.HdfsAtomicWritePipe('my_file')
    pipe.writeLine('Hello')
    pipe.abort()
    pipe.writeLine('world')
    pipe.close()