tests/kernel/context: don't do print in time-critical section

In test_busy_wait and test_k_sleep test cases of
tests/kernel/context test we measure not only execution time of the
primitives itself (k_busy_wait and k_msleep respectively) but also
the overall test thread execution time.

The issue here is that we do printing in test threads which
means that we do printing in time-critical sections. That breaks
test if we do printing via some device which isn't fast enough.

Fix that by removing print from time-critical section

Signed-off-by: Evgeniy Paltsev <PaltsevEvgeniy@gmail.com>
Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>