tests: kernel: added memory slab concept test

TestPurpose: verify memory pool concepts.
All TESTPOINTs extracted from kernel documentation.
https://www.zephyrproject.org/doc/kernel/memory/slabs.html#concepts



ZEP-1209

Change-Id: I95c6cd666212218b9928356f9439e67a2fcf9b73
Signed-off-by: Sharron LIU <sharron.liu@intel.com>