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.

MFC various fixes for the ATF tests.

- r260505 Allow tests to provide a Kyuafile when they relied on auto-generation.
- r260525 Respect the original layout of the atf-{c,c++} tests.
- r260526 Fix path to the process_helpers for the libatf-c++ tests.
- r260576 Generate and install pkg-config files for atf.
- r260577 Add atf pkg-config files from the vendor branch.
- r260584 Prevent misc_helpers from running as a test.

Plug the ATF tests into the build.

This is a MFC into stable/10 of:
- r257849 Add libatf-c++ to the prebuild libs.
- r257853 Build and install the atf tests.
- r258233 Move all atf directories to the tests mtree.
- r258285 Fix the build of some ATF tests.

This change is "make tinderbox" clean on ref10-amd64 with the default
settings of WITHOUT_TESTS. It is likely for the WITH_TESTS build to
still be broken because not all relevant changes have been merged yet.

Build and install the atf tests.

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