Avoid unnecessary logging on anonymous access.

[ksauzz]

We shouldn't output no_user_key error on proper anonymous access such as getting a public object.

2014-05-29 18:08:35.835 [error] <0.2515.0>@riak_cs_wm_common:maybe_create_user:218 Retrieval of user record for s3 failed. Reason: no_user_key

[shino]

For example, if one use riak_cs for file download with public read ACL, this log can happen heavily. Lager, by default setting, calls file:datasync/1 for error or higher severity [1]. So this issue may increase disk load.

[1] https://github.com/basho/lager/blob/master/src/lager_file_backend.erl#L228

[shino]

Move to 1.5.0

[shino]

Resolved by #883.