'send object POST request to storage nodes.
:param req: the POST Request
:param obj_ring: the object ring
:param partition: ring partition number
:param headers: system headers to storage nodes
:return: Response object'

def _post_object(self, req, obj_ring, partition, headers):

    resp = self.make_requests(req, obj_ring, partition, 'POST', req.swift_entity_path, headers)
    return resp
