tests: Add test for microkernel early sleep functionality

Test verifies that a task_sleep() function can be used during the system
initialization, then it tests that when the k_server() starts, task_sleep()
call makes another task run.

For fibers, test that fiber_sleep() called during the system
initialization puts a fiber to sleep for the provided amount of ticks,
then check that fiber_sleep() called from a fiber running on the
fully functioning microkernel puts that fiber to sleep for the proiveded
amount of ticks.

Change-Id: Iec20b61d7e802a19b1ec074d2511345eed9f2407
Signed-off-by: Dmitriy Korovkin <dmitriy.korovkin@windriver.com>