kunit: add example suite to test init suites

Add example_init_test_suite to allow for testing the feature of running
test suites marked as init to indicate they use init data and/or
functions.

This suite should always pass and uses a simple init function.

This suite can also be used to test the is_init attribute introduced in
the next patch.

Signed-off-by: Rae Moar <rmoar@google.com>
Reviewed-by: David Gow <davidgow@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>