Change GS calls to make_request to always convert to utf-8 bytes.

Previously, if the body string was encoded as bytes but a parameter (e.g. key
name) was a unicode string, the underlying httplib/socket layer would get
unicode decode errors when the mixing would force a unicode cast.
Merge pull request #1421 from jterrace/fix-bucket-unicode-issue

Change GS calls to make_request to always convert to utf-8 bytes.