This patch fixes bug #1221087.
Replaces time.mktime() to calendar.timegm() in utils.unixtime()
to get correct expiration time.
After this patch, Memcached token backend does not depend on timezone.
So remove the section "Memcached and System Time" in configuration manual.
DocImpact
Change-Id: I17233c8a79d01a37abdbd46934ad486ddc8caec9