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.

Update atf to 0.18 and remove the code of the deprecated tools.

This is a MFC into stable/10 of:
- r258286 Update notes for imports of atf.
- r258289 MFV: Import atf-0.18.
- r258290 Drop all ATF tools code.

This is "make tinderbox" clean as run on ref10-amd64 with the default
WITHOUT_TESTS option. A "make buildworld" with WITH_TESTS set now works
as well.

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)