Updated openstack/openstack
Project: openstack/oslo.i18n  a538a3bacf2c4839039947613697956f124904ef

Make clear in docs to use _LE() when using LOG.exception()

Added note to guidelines.rst about this case and added an example
in usage.rst.

Closes-Bug: #1378053
Change-Id: Ie29441e0f354aab2b04d731dc5d597390b89783d