tests: kernel: Stress test for preemptive scheduling.

Tests if preemptive threads are picked up as per priority.
This creates 10 threads with priority in increasing order
from 1 to N and each thread prints an Alphabet.
This test fails when threads are picked up out of order.

Jira: ZEP-2370

Signed-off-by: Youvedeep Singh <youvedeep.singh@intel.com>