perf test: Add a signal handler to kill forked child processes

perf test: Add a signal handler to kill forked child processes

If the `perf test` process is killed the child tests continue running
and may run indefinitely. Propagate SIGINT (ctrl-C) and SIGTERM (kill)
signals to the running child processes so that they terminate when the
parent is killed.

Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Colin Ian King <colin.i.king@gmail.com>
Cc: Howard Chu <howardchu95@gmail.com>
Cc: Weilin Wang <weilin.wang@intel.com>
Cc: James Clark <james.clark@linaro.org>
Cc: Ilya Leoshkevich <iii@linux.ibm.com>
Cc: Thomas Richter <tmricht@linux.ibm.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Dapeng Mi <dapeng1.mi@linux.intel.com>
Cc: Athira Jajeev <atrajeev@linux.vnet.ibm.com>
Cc: Michael Petlan <mpetlan@redhat.com>
Cc: Veronika Molnarova <vmolnaro@redhat.com>
Link: https://lore.kernel.org/r/20241025192109.132482-10-irogers@google.com
Signed-off-by: Namhyung Kim <namhyung@kernel.org>