tests: kernel: alert: Add testcases

Add testcases for following scenario

Test to check alert_recv(timeout) against the following cases

1. The current task times out while waiting for the event.
2. There is already an event waiting (signalled from a task).
3. The current task must wait on the event until it is signalled
   from either another task or an ISR

Test to check alert_recv(K_FOREVER) against the following cases:

1. There is already an event waiting (signalled from a task and ISR).
2. The current task must wait on the event until it is signalled
   from either another task or an ISR

Test to checks that the event handler is set up properly when
alert_event_handler_set() is called.  It shows that event handlers
are tied to the specified event and that the return value from the
handler affects whether the event wakes a task waiting upon that
event

Signed-off-by: Savinay Dharmappa <savinay.dharmappa@intel.com>