added "itti_exit_task" to terminate current task when a MESSAGE_TERMINATE is received.

Modified "itti_wait_tasks_end" to exit when some threads are not terminated after a 1 second time-out.
modified "SIGINT" handling, exit is done after tring to join all threads like for "SIGUSR1".
Added message reception for TASK_L2L1 and handling of TEST and TERMINATE messages in oaisim.

git-svn-id: http://svn.eurecom.fr/openair4G/trunk@4269 818b1a75-f10b-46b9-bf7c-635c3b92a50f