Arvados

Example:

>>> import arvados
>>> x = 'x' * 67108865
>>> len(x)
67108865
>>> hash = arvados.keep.KeepClient().put(x)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python2.7/dist-packages/arvados/retry.py", line 157, in num_retries_setter
    return orig_func(self, *args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/arvados/keep.py", line 719, in put
    (data_hash, copies, thread_limiter.done()))
arvados.errors.KeepWriteError: Write fail for 66e31f9f0968774cf4cb2dac211054b0: wanted 2 but wrote 0

While this isn't an operation we should expect to succeed, it would be useful for the user if KeepClient returned a more helpful error message.