MFC r289172,r290254:

r289172:

Refactor the test/ Makefiles after recent changes to bsd.test.mk (r289158) and
netbsd-tests.test.mk (r289151)

- Eliminate explicit OBJTOP/SRCTOP setting
- Convert all ad hoc NetBSD test integration over to netbsd-tests.test.mk
- Remove unnecessary TESTSDIR setting
- Use SRCTOP where possible for clarity

r290254:

Remove unused variable (SRCDIR)

MFC r264741: Add placeholder Kyuafiles for various top-level hierarchies.

This is "make tinderbox" clean.

Add placeholder Kyuafiles for various top-level hierarchies.

This change adds tests/ directories in the source tree to create various
subdirectories in /usr/tests/ and to install placeholder Kyuafiles for
them.

the relevant hierarchies are: cddl, etc, games, gnu and secure.

The reason for this is to simplify the addition of new test programs for
utilities or libraries under any of these directories. Doing so on a
case by case basis is unnecessary and is quite an obscure process.