fake_log_device: long lived allocations

Use static space for long lived allocations as they
will appear to act like a memory leak. Resort to a
larger on-stack iovec to reduce the chances of an
allocation. Fix bug in writer where not enough size
was available for "security" buffer name. Minor
transitions to more consistent coding style.

Bug: 27107691
Change-Id: I68c918e7b916b1ae3b04829d48b3eddaa0a7e739