Pydoop submit: allow dist cache items from HDFS

[simleo]

pydoop submit simplifies adding items to the DC via --upload-{file,archive}-to-cache. These items are looked for in the local fs, and are automatically uploaded to temporary HDFS locations before adding them to the DC. While this is usually what the user wants, this feature should also be able to handle items already on HDFS.

Option names can change to --cache-{files,archive} (do this before Pydoop 2.0 final), since their actions won't necessarily involve an upload anymore.