Regression test for vn_io_fault

[Konstantin Belousov]

On Wed, Jun 05, 2019 at 10:29:35AM -0600, Alan Somers wrote:
> r236321 added vn_io_fault(), a mechanism for avoiding lock order
> reversals when a process reads from one file into a mmap()ed buffer
> backed by another file.  From the description in the comments of
> vn_io_fault() it seems like it would be possible to write a reliable
> test that would trigger the LOR.  But I can't find any evidence in
> svn, or bugzilla of such a test program.  None in Phabricator either,
> which probably wasn't even running when that commit was made.  Did
> anybody ever write a test program?  If so, I volunteer to ATFify it.
The test program is in tools/test/upsdl. I object against removing
non-atf version on principle, atf tests are not debuggable. Also this is
racing test, so it is not as simple as doing N runs where N is fixed.

Anyway, test for the ups@ race is included into stress2, where it belongs.