ftracetest: Clear trace buffer after running kprobe testcases

The kprobe testcases create, use and delete dynamic events during the
test but didn't clear the trace buffer so it'll leave the result after
it finishes.

  # ./ftracetest
  ...

  # cat trace
  # tracer: nop
  #
  # entries-in-buffer/entries-written: 2/2   #P:12
  #
  #                              _-----=> irqs-off
  #                             / _----=> need-resched
  #                            | / _---=> hardirq/softirq
  #                            || / _--=> preempt-depth
  #                            ||| /     delay
  #           TASK-PID   CPU#  ||||    TIMESTAMP  FUNCTION
  #              | |       |   ||||       |         |
        ftracetest-26474 [009] d..1 79417.143782: Unknown type 1099
        ftracetest-26498 [009] d..1 79417.208034: Unknown type 1101

Link: http://lkml.kernel.org/r/1415239470-28705-2-git-send-email-namhyung@kernel.org

Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

tools/testing/selftests/ftrace/test.d/kprobe/add_and_remove.tc

@@ -9,3 +9,4 @@ echo p:myevent do_fork > kprobe_events
 grep myevent kprobe_events
 test -d events/kprobes/myevent
 echo > kprobe_events
+clear_trace

tools/testing/selftests/ftrace/test.d/kprobe/busy_check.tc

@@ -11,3 +11,4 @@ echo 1 > events/kprobes/myevent/enable
 echo > kprobe_events && exit 1 # this must fail
 echo 0 > events/kprobes/myevent/enable
 echo > kprobe_events # this must succeed
+clear_trace

tools/testing/selftests/ftrace/test.d/kprobe/kprobe_args.tc

@@ -12,5 +12,6 @@ echo 1 > events/kprobes/testprobe/enable
 ( echo "forked")
 echo 0 > events/kprobes/testprobe/enable
 echo "-:testprobe" >> kprobe_events
+clear_trace
 test -d events/kprobes/testprobe && exit 1 || exit 0
 

tools/testing/selftests/ftrace/test.d/kprobe/kretprobe_args.tc

@@ -12,4 +12,5 @@ echo 1 > events/kprobes/testprobe2/enable
 ( echo "forked")
 echo 0 > events/kprobes/testprobe2/enable
 echo '-:testprobe2' >> kprobe_events
+clear_trace
 test -d events/kprobes/testprobe2 && exit 1 || exit 0