Previously the only way to use lockfree implementation was to start executable and never switch to guarded allocator. Surely, it is not possible to switch implementation once any allocation did happen, but some tests are desired to test lock-free implementation of the allocator. Those tests did not operate properly because the main entry point of tests are forcing guarded allocator to help catching bugs. This change makes it possible for those tests to ensure they do operate on lock-free implementation. There is no functional changes here, preparing boilerplate for an upcoming work on the allocator tests themselves.