Use oslo libraries - i18n and utils

Remove the files synced from oslo-incubator and adjust
the openstack-common.conf. Note that _message.Message extends
six.text_type so we don't need the extra condition check in
jsonutils.py. Tests have been updated to use the fixture in
i18n 0.2.0 to avoid directly referring to private modules.

Change-Id: I971df3a154317a5dff93c83143092c98023b84c9