Disable malloc debug intercepts when exiting.

There is a hang when enabling leak_track since the dumping of the
leak data can wind up doing an allocation.

Add new system unit test to make sure this doesn't happen again.

Bug: 111146059

Test: Test program that leaks does not hang forever.
Test: Unit tests pass.
Change-Id: Icf99be58ba5db98ee124a471b957a086045f5870