[3.15] gh-151496: Use process groups in TraceBackend in test_dtrace (GH-152039) ...

[3.15] gh-151496: Use process groups in TraceBackend in test_dtrace (GH-152039) (#152082)

gh-151496: Use process groups in TraceBackend in test_dtrace (GH-152039)

Run the generic DTrace/SystemTap commands in a new process group and
terminate the whole group on timeout.

This prevents a forked tracer child from keeping stdout/stderr pipes
open after the direct tracer process is killed.
(cherry picked from commit 1785f4b35f899704df0be54cba3776906186b2b1)

Co-authored-by: stratakis <cstratak@redhat.com>