perf evlist: Reset SIGTERM handler in workload child process

Jiri reported hanging perf tests on latest acme's perf/core and bisected
it to 87f303a9f:

[jolsa@krava2 perf]$ cat /proc/sys/kernel/perf_event_paranoid
1
[jolsa@krava2 perf]$ ./perf record -C 0 kill
Error:
You may not have permission to collect %sstats.
Consider tweaking /proc/sys/kernel/perf_event_paranoid:
 -1 - Not paranoid at all
  0 - Disallow raw tracepoint access for unpriv
  1 - Disallow cpu events for unpriv
  2 - Disallow kernel profiling for unpriv

Need to let default handling kickin for workload process.
Reported-by: Jiri Olsa <jolsa@redhat.com>
Signed-off-by: David Ahern <dsahern@gmail.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Tested-by: Jiri Olsa <jolsa@redhat.com>
Link: http://lkml.kernel.org/r/1369525839-1261-1-git-send-email-dsahern@gmail.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/evlist.c

@@ -776,6 +776,8 @@ int perf_evlist__prepare_workload(struct perf_evlist *evlist,
 		if (pipe_output)
 			dup2(2, 1);
 
+		signal(SIGTERM, SIG_DFL);
+
 		close(child_ready_pipe[0]);
 		close(go_pipe[1]);
 		fcntl(go_pipe[0], F_SETFD, FD_CLOEXEC);