Properly catch and restore timezone

Part of request #7466 Tuleap test suite should run on php 5.4 and onward

Change-Id: Idd76d3c0d895fbc91d9e3bb374f989a95db20f0a
Merge commit 'refs/changes/47/2947/2' of ssh://gerrit.tuleap.net:29418/tuleap into stable

* ssh://gerrit.tuleap.net:29418/tuleap:
  Properly catch and restore timezone
This is Tuleap 7.5.99.39

Change-Id: I0b890105c048cd1a327edf07dd01145aa90b4c46