Add 'Z' into isoformat for UTC time

Based on this http://en.wikipedia.org/wiki/ISO_8601#Time_zone_designators.
A isofomt of time need a 'Z' for UTC time zone, or none for local time zone

request on GET /<version>/<account>/<container>?format=json still output a
UTC time without 'Z'

fixes bug #1169287
Change-Id: Ib599b5ec8fd223878ec18df7c1ec8d952fc2630a
Merge "Add 'Z' into isoformat for UTC time"