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.