kunit: improved sigsegv stack trace printing

Sacrificed the control of printing stack trace within the crash handler
in the test runner for getting a better stack trace; this is still not
ideal, but much better than before.

Change-Id: I9b58ed736733895aa3ededc3829637c4271d91c1
Signed-off-by: Brendan Higgins <brendanhiggins@google.com>