Because the direct_client module uses the buffered_http module it's
requests are already robust to receiving either unicode or utf-8 paths.
The DirectClientException message however encodes the given path with
the device key from a ring node - which having come from a json
de-serialized ring will be a unicode type. Despite the device key
almost always being only ascii characters; python string interpolation
with any unicode type will always force all binary strings to be
converted to unicode - which will raise an error if any byte strings
includes non-ascii characters.
To maintain robustness in DirectClientException, when the provided path
is not already unicode we decode the bytes as utf-8 before mixing them
with the other unicode strings and then normalize everything back to a
quoted utf-8 byte string.
Change-Id: I162d2e093a3110856d6e1d513de3c7919079c9e7
87eaaebd67