gh-ost: Timezone issue with timestamp columns if server doesn't use UTC.

After running a gh-ost with -test-on-replica I found differences in two timestamp columns.

I found this by doing a

select 
  * 
from 
  t1 a 
  inner join _t1_gho b on a.id=b.id 
where 
  a.c1<>b.c1 
  or a.c2<>b.c2
  ...

Record 1

   timestamp_notified: 2016-08-17 13:08:04
   timestamp_notified: 2016-08-17 11:08:04

Record 2

   timestamp_notified: 2016-08-17 13:08:19
  timestamp_finalized: 2016-02-01 23:39:30
   timestamp_notified: 2016-08-17 11:08:19
  timestamp_finalized: 2016-02-01 22:39:30

From the definition:

  `timestamp_notified` timestamp NULL DEFAULT NULL,
  `timestamp_exported` timestamp NULL DEFAULT NULL,
  `timestamp_finalized` timestamp NULL DEFAULT NULL,