bucket files: Change static attributes to non static. Call right
constructor for s3.

* src/dctc/java/com/dataiku/dctc/file/BucketBasedFile.java: Here.
* src/dctc/java/com/dataiku/dctc/command/Ls.java,
  src/dctc/java/com/dataiku/dctc/file/GSFile.java,
  src/dctc/java/com/dataiku/dctc/file/S3File.java: Adjust.
gs: Correct bucket name.

* src/dctc/java/com/dataiku/dctc/file/GSFile.java: Set the correct
  bucket name.