perf test: Silence tracepoint event failures

Currently, when 'perf test' is run by a normal user, it'll fail to
access tracepoint events.  The output becomes somewhat messy because it
tries to be nice with long error messages and hints.

IMHO this is not needed for 'perf test' by default and AFAIK 'perf test'
uses pr_debug() rather than pr_err() for such messages so that one can
use -v option to see further details on failed testcases if needed.

Before:
  $ perf test
   1: vmlinux symtab matches kallsyms                          : FAILED!
   2: detect openat syscall event                              :Error:
  No permissions to read
  /sys/kernel/debug/tracing/events/syscalls/sys_enter_openat
  Hint:	Try 'sudo mount -o remount,mode=755 /sys/kernel/debug/tracing'
  FAILED!
   3: detect openat syscall event on all cpus                  :Error:
  No permissions to read
  /sys/kernel/debug/tracing/events/syscalls/sys_enter_openat
  Hint:	Try 'sudo mount -o remount,mode=755 /sys/kernel/debug/tracing'
  FAILED!
   ...

After:
  $ perf test
   1: vmlinux symtab matches kallsyms                          : FAILED!
   2: detect openat syscall event                              : FAILED!
   3: detect openat syscall event on all cpus                  : FAILED!
   ...

  $ perf test -v 2
   2: detect openat syscall event                              :
  --- start ---
  test child forked, pid 30575
  Error:	    No permissions to read
  /sys/kernel/debug/tracing/events/syscalls/sys_enter_openat
  Hint:  Try 'sudo mount -o remount,mode=755 /sys/kernel/debug/tracing'

  test child finished with -1
  ---- end ----
  detect openat syscall event: FAILED!

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Acked-by: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/r/1445268229-1601-1-git-send-email-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/tests/openat-syscall-tp-fields.c

@@ -89,7 +89,7 @@ int test__syscall_openat_tp_fields(void)
 
 				err = perf_evsel__parse_sample(evsel, event, &sample);
 				if (err) {
-					pr_err("Can't parse sample, err = %d\n", err);
+					pr_debug("Can't parse sample, err = %d\n", err);
 					goto out_delete_evlist;
 				}