test: fix incorrect resource release

There were two problems with resource release in performance test:
- because of manually zeroing of `box_tuple_last`, tuple_format
  structure was not deleted. `box_tuple_last` should be zeroed in
  `tuple_free` function.
- invalid loop for resource release in one of the test cases.
This patch fix both problems.

NO_CHANGELOG=test fix
NO_DOC=test fix