test: scheduling: add configuration item

When using Red/black tree ready queue as scheduling algorithm,
there are no limit to the number of priority levels. So set the
CONFIG_NUM_COOP_PRIORITIES to 30, testcase test_bad_prooritiesi()
will prove both cooperative and preemptive thread have no quantitative
limit.

Signed-off-by: Ying ming <mingx.ying@intel.com>