tests: make both Valgrind and LeakSanitizer happy

The talloc_enable_null_tracking() actually allocates a new talloc
context, which makes both Valgrind and LeakSanitizer angry. This
context should be freed by the talloc_disable_null_tracking().

Change-Id: Ia660d2fdac720f685c0186720d0a476d7e9468be
4 files changed