[Orchestrator] - taskGateway compare lastExec in UTC format with a variable now - set without arg, taking local time instead

We must change line 309 of tastGateway to be sure to generate a now time in UTC. We could have used Unix timestamp (always generated in UTC) but dateTime object are easy to use.

Let's change line 309

      // Is used to verify cyclic schedule with date format.
      $now = new DateTime();

with

$now = new DateTime('now', new DateTimeZone('UTC'));