Fix "run_all_unit_tests.sh" grep pattern

Grep for "FAIL" and not "FAIL:" because not all failing test cases
output "FAIL:". For example 'TEST_FAIL()' leads to "<test case>:FAIL"
'awaitStimuli()' attempt to read from master thrice

System wrapper for 'sleep()' function added because there needs to be
a wait time inbetween read attempts