no call stacks in hung CI runs

[Bruce Schuchardt]

I'm trying to figure out why my stress-tests are hanging in CI but not 
when I run the tests locally.  The artifacts have a "callstacks" 
directory but there aren't any thread dumps that I've been able to locate.

callstacks> ls
callstacks-2018-12-20-02-16-27.txt callstacks-2018-12-20-02-16-40.txt
callstacks-2018-12-20-02-16-33.txt dunit-hangs.txt
No thread dumps in these files and test output is useless since things 
are running in parallel and writing to the same output stream.