ion-unit-tests: Add system heap presence test

Make sure system heap is present on devices, its id is '0',
and that we can allocate and free buffers from the system heap

Bug: 140507100
Fixes: 140507100
Tests: ion-unit-tests --gtest_fiter=SystemHeap.*

Change-Id: Ief502c9fce1e54f54b4e6d60f288954e4bf42e04
Signed-off-by: Sandeep Patil <sspatil@google.com>