adjust metadata.py to use 4 spaces indent
only return user metadata for cdmi ?metadata queries

change the logic to return metadata. now stat() returns
all metadata, system and user. get_user_metadata only
fetches user metadata, which is what ?metadata should return.

get_user_metadata and a stub for set_user_metadata are added
to metadata.py, which calls equivalent functions in the storage.py.

These functions are now only added to the irods backend.
adjust storage.py to 4spaces
adjust irods storage file to 4 spaces indent
change function name to adhere to python private func guidelines

change the func name of irodsstorage._get_user_metadata to
__get_user_metadata