Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

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

Copy README into /usr/tests

Add a few sentences describing how to run the tests.

Reviewed by: ngie
Differential Revision: https://reviews.freebsd.org/D4224

Install category Kyuafiles from their category directories.

Move the installation of /usr/tests/lib/Kyuafile from src/tests/lib/
to src/lib/. This is to keep the src/tests/ hierarchy unaware of the
rest of the tree, which makes things clearer in general. In particular:

1) Everything related to the construction of /usr/tests/lib/ is kept
in src/lib/. There is no need to think about different directories
and how they relate to each other. (The same applies for libexec,
usr.bin, etc. but these are not yet handled.)

2) src/tests becomes the place to keep cross-functional test programs
and nothing else, which also helps in simplifying things.

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

Set up the /usr/tests hierarchy.

Populate /usr/tests with the only test programs that currently live
in the tree (those in lib/libcrypt/tests/) and add all the build
machinery to accompany this change.

In particular:

- Add a WITHOUT_TESTS variable that users can define to request that
no tests be put in /usr/tests.
- Add a top-level Kyuafile for /usr/tests and a way to create similar
Kyuafiles in top-level subdirectories.
- Add a BSD.tests.dist file to define the directory layout of
/usr/tests.

Submitted by: Julio Merino jmmv google.com
Reviewed by: sjg
MFC after: 2 weeks