Fix error condition output of streaming operations to have binary() reason [RTS-1602]

[paegun]

Reviewers (if I may suggest):

• @fadushin Please review since you peered into the regression test failure for a bit before.
• @alexmoore or @lukebakken being the resident erlang client experts, please review as well.

Summary: This fixes regression test break riak_test verify_api_timeouts.

Features:

• fixed error condition output of streaming operations expected to be in the form {error, binary()}, but was {error, atom()}.

[lukebakken]

The test has been unchanged since 4/18/2013: https://github.com/basho/riak_test/commit/4b8d8358611962caffe7c09935dc434620835149

I'm going to figure out where the regression was introduced in the client or server. I don't think this is the right fix.

[paegun]

@lukebakken found the underlying riak-erlang-client (riakc) issue and will PR that instead, so closing.