tests: specify the timezone offset

tests: specify the timezone offset

On mingw (Windows) EST alone resolve to UTC since windows does not
recognize EST.

We could also use "America/Toronto" but this would require more change
to the test. Since this test is only there to test the TZ usage the
actual value of TZ does not matter. UTC5 would have done the same job.

Signed-off-by: Jonathan Rajotte <jonathan.rajotte-julien@efficios.com>
Change-Id: I05270504c69a90d4e9893435d1c1b583579041ae
Reviewed-on: https://review.lttng.org/c/babeltrace/+/1662
Reviewed-by: Michael Jeanson <mjeanson@efficios.com>
Reviewed-by: Philippe Proulx <eeppeliteloop@gmail.com>
Tested-by: jenkins <jenkins@lttng.org>