Return date/time in UTC in JMX connector

[findepi]

Using server zone introduces ambiguity problem during DST change.
Presto engine has no problem representing and distinguishing
(point-in-time, zone) pairs regardless of DST. However, due to
how they are formatted for the client, client can no longer distinguish
values within summer→winter DST change.

In the example below, rows with increment 1 and 2 represent different
point in time, but are rendered the same for the client.

presto> SELECT
     ->     increment,
     ->     from_unixtime(base + increment * 3600, 'America/Los_Angeles')
     -> FROM (VALUES(1572766200)) t(base)
     -> CROSS JOIN UNNEST(sequence(0, 3)) u(increment);
     ->
 increment |                    _col1
-----------+---------------------------------------------
         0 | 2019-11-03 00:30:00.000 America/Los_Angeles
         1 | 2019-11-03 01:30:00.000 America/Los_Angeles
         2 | 2019-11-03 01:30:00.000 America/Los_Angeles
         3 | 2019-11-03 02:30:00.000 America/Los_Angeles
(4 rows)