kunit: add example test case showing off all the expect macros

Currently, these macros are only really documented near the bottom of
https://www.kernel.org/doc/html/latest/dev-tools/kunit/api/test.html#c.KUNIT_FAIL

.

E.g. it's likely someone might just not realize that
KUNIT_EXPECT_STREQ() exists and instead use KUNIT_EXPECT_FALSE(strcmp())
or similar.

This can also serve as a basic smoketest that the KUnit assert machinery
still works for all the macros.

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