test_pool: exclude on olimexino_stm32 and nucleo_f103rb

These two boards don't have enough RAM to effectively run this
test case without making the stacks so small they don't work
on other platforms. ARM is sill covered by other boards.

Change-Id: Ibf20eefaf29f989cbb6da6cd3a8eeed2faa1950b
Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>