Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

MFC refactoring of the *.test.mk files.

- r263161 Make bsd.test.mk the only public mk fragment for the building of tests.
- r263172 Move FreeBSD Test Suite-specific code to a suite.test.mk file.
- r263204 Add some documentation for bsd.test.mk.
- r263217 Document support for TAP-compliant Perl test programs.

This is "make tinderbox" clean.

Move FreeBSD Test Suite-specific code to a suite.test.mk file.

The new suite.test.mk file contains all the logic needed to install test
programs under /usr/tests/ and to support Kyua as the run-time engine.
This file is included by default by bsd.test.mk so Makefiles do not need
to care about its existence.

Specific Makefiles can define NOT_FOR_TEST_SUITE to indicate that whatever
test programs they are building are not supposed to be installed under
/usr/tests/ nor run by Kyua. (The effect of passing this setting is that
suite.test.mk is simply not included.)

NOT_FOR_TEST_SUITE should never be used by Makefiles in the base system.
This functionality is provided so that third-parties can hook in their
own test code, with different semantics, if they wish. This was asked
for by sjg@.