This adds wsgi_to_str(self.path_info) everywhere we forgot it,
not only in the slo module itself.
Dropping the body=''.join(body) after call_slo() is obvious:
the latter only returns strings of bytes, not lists of such.
Change-Id: I6b4d87e4cda4945bc128dbc9c1edd39e736a59d2
bd8c3067b4