test/mempool: support default mempool
test/mempool: support default mempool

Mempool test currently supports:
 * ring_mp_mc
 * stack

Adding a new default pool options. So, ring* + stack + default
(which can be 'stack' or 'ring')
 * This way, whatever the value of RTE_MBUF_DEFAULT_MEMPOOL_OPS is set,
   it would be verified.
 * even if that means duplicating some test (for example when "stack" is
   set as default and it already part of standard test)

Signed-off-by: Shreyansh Jain <9744844f062a9f6cf95f66f06508da54c8fc7929@nxp.com>
Reviewed-by: Santosh Shukla <23b682afe3504ae4f88c66c3cabfb34f87e9916e@caviumnetworks.com>
Acked-by: Olivier Matz <dfcc1510895413197abb4336e39bb0a3906cba71@6wind.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk