[OMPT] Fix ompt_get_task_info() and add tests for it

The thread_num parameter of ompt_get_task_info() was not being used previously,
but need to be set.

The print_task_type() function (form the task-types.c testcase) was merged into
the print_ids() function (in callback.h). Testing of ompt_get_task_info() was
added to the task-types.c testcase. It was not tested extensively previously.

Differential Revision: https://reviews.llvm.org/D42472

llvm-svn: 326338