Revert passing content body to http request (minio#619)

This change was intended for go 1.8 but it is too
early to switch to the new version of go.

api.go

@@ -588,7 +588,7 @@ func (c Client) newRequest(method string, metadata requestMetadata) (req *http.R
 	}
 
 	// Initialize a new HTTP request for the method.
-	req, err = http.NewRequest(method, targetURL.String(), metadata.contentBody)
+	req, err = http.NewRequest(method, targetURL.String(), nil)
 	if err != nil {
 		return nil, err
 	}
@@ -608,6 +608,11 @@ func (c Client) newRequest(method string, metadata requestMetadata) (req *http.R
 		return req, nil
 	}
 
+	// Set content body if available.
+	if metadata.contentBody != nil {
+		req.Body = ioutil.NopCloser(metadata.contentBody)
+	}
+
 	// FIXME: Enable this when Google Cloud Storage properly supports 100-continue.
 	// Skip setting 'expect' header for Google Cloud Storage, there
 	// are some known issues - https://github.com/restic/restic/issues/520