Bug fixes: OMPT corner cases (unsafe way to free parallel region's team)

[vladaindjic]

Temporary solution for two bugs:

1. parallel_data at level 0 present, but not at outer levels (1, 2, etc.), even though there are few levels of nested regions. Reason: The descriptor of the innermost parallel region invalidates the pointer to parent region too early.
2. The same region descriptor may be passed multiple times to ompt_callback_parallel_end. Reason: Using (sending to the ompt_callback_parallel_end) pointer to the field of region's descriptor which was previously put in the free list.

Examples that described temporary resolved bugs can be found in the comments in source code.