Ensure that tests are always executed in a proper time zone (#2551)

The America/Los_Angeles time zone is already enforced for test262
Travis CI jobs but that doesn't guarantee the correctness of
locally executed tests. So, this patch moves the setting of the
`TZ` environment variable from `.travis.yml` to `run-tests.py`.

The date-related tests in the jerry test suite also rely on a time
zone (UTC). Thus, `TZ` is forced for those tests, too.

JerryScript-DCO-1.0-Signed-off-by: Akos Kiss akiss@inf.u-szeged.hu

.travis.yml

@@ -72,7 +72,6 @@ matrix:
     - env:
         - JOBNAME="Conformance Tests"
         - OPTS="--test262"
-        - TZ=America/Los_Angeles
 
     - env:
         - JOBNAME="ASAN Tests"