kunit: test: Add example tests which are always skipped

Add two new tests to the example test suite, both of which are always
skipped. This is used as an example for how to write tests which are
skipped, and to demonstrate the difference between kunit_skip() and
kunit_mark_skipped().

Note that these tests are enabled by default, so a default run of KUnit
will have two skipped tests.

Signed-off-by: David Gow <davidgow@google.com>
Reviewed-by: Daniel Latypov <dlatypov@google.com>
Reviewed-by: Brendan Higgins <brendanhiggins@google.com>
Reviewed-by: Marco Elver <elver@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>