Runing most of isisd tests with --valgrind-memleaks give many memory errors.
This is due to the way isisd is stopped: performing a "no router isis XXX"
through CLI solves most of them. Indeed, isis_finish() doesn't call
isis_area_destroy() leaving many allocated memory unfreed.
This patch adds call to appropriate delete function or XFREE() when necessary to
properly free all alocated memory before terminating isisd.