crypto/scheduler: add unit test

crypto/scheduler: add unit test

Same as other cryptodev PMDs, it is necessary to carry out the unit
test for scheduler PMD. Currently the test is designed to attach 2
AESNI-MB cryptodev PMDs as slaves, sets the scheduling mode as round-
robin, and runs almost all AESNI-MB test items (except for sessionless
tests). In the end, the slaves are detached.

Signed-off-by: Fan Zhang <roy.fan.zhang@intel.com>
Acked-by: Pablo de Lara <pablo.de.lara.guarch@intel.com>