perf test attr: Fix ignored test case result

Command perf test -v 16 (Setup struct perf_event_attr test) always
reports success even if the test case fails.  It works correctly if you
also specify -F (for don't fork).

   root@s35lp76 perf]# ./perf test -v 16
   15: Setup struct perf_event_attr               :
   --- start ---
   running './tests/attr/test-record-no-delay'
   [ perf record: Woken up 1 times to write data ]
   [ perf record: Captured and wrote 0.002 MB /tmp/tmp4E1h7R/perf.data
     (1 samples) ]
   expected task=0, got 1
   expected precise_ip=0, got 3
   expected wakeup_events=1, got 0
   FAILED './tests/attr/test-record-no-delay' - match failure
   test child finished with 0
   ---- end ----
   Setup struct perf_event_attr: Ok

The reason for the wrong error reporting is the return value of the
system() library call. It is called in run_dir() file tests/attr.c and
returns the exit status, in above case 0xff00.

This value is given as parameter to the exit() function which can only
handle values 0-0xff.

The child process terminates with exit value of 0 and the parent does
not detect any error.

This patch corrects the error reporting and prints the correct test
result.

Signed-off-by: Thomas-Mich Richter <tmricht@linux.vnet.ibm.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Thomas-Mich Richter <tmricht@linux.vnet.ibm.com>
LPU-Reference: 20170913081209.39570-2-tmricht@linux.vnet.ibm.com
Link: http://lkml.kernel.org/n/tip-rdube6rfcjsr1nzue72c7lqn@git.kernel.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>