For UTs mbed_assert_internal should not be declared as MBED_NORETURN
as UT stub for mbed_assert_internal only prints out the assert trace
and returns back to original code.
-Added the mock class function to mock mbed_assert_internal
-Added the unit test case to test start,kick,stop
-Modified the interface api name from is_alive to process
-added the unit test cases for process