commands: stop using exception.message attribute, it's deprecated
files: change variable name
filesystem: make rm_rf() work on linux

os.remove() raises on linux.
(This is the non-POSIX value returned by Linux since 2.1.132.)
files: better __repr__ for RenamableFile
files: use pytest on tests
files: RenamableFile implement chunks()
test helpers: move method to function
bulkupload: use pytest on tests
bulkupload: ignore image versions local, they will be generated
bulk_upload: don't fail if CUMULUS setting is not present

this setting is only use for the rackspace storage.
images: better __repr__ method for out ImageFile subclass
storage/filesystem: add __repr__