Migrate tools/regression/bin/ tests to the new layout.

This change is a proof of concept on how to easily integrate existing
tests from the tools/regression/ hierarchy into the /usr/tests/ test
suite and on how to adapt them to the new layout for src.

To achieve these goals, this change:

- Moves tests from tools/regression/bin/<tool>/ to bin/<tool>/tests/.
- Renames the previous regress.sh files to legacy_test.sh.
- Adds Makefiles to build and install the tests and all their supporting
  data files into /usr/tests/bin/.
- Plugs the legacy_test test programs into the test suite using the new
  TAP backend for Kyua (appearing in 0.8) so that the code of the test
  programs does not have to change.
- Registers the new directories in the BSD.test.dist mtree file.

Reviewed by:	freebsd-testing
Approved by:	rpaulo (mentor)