kselftests/ftrace : Add event trigger testcases

kselftests/ftrace : Add event trigger testcases

This adds simple event trigger testcases for ftracetest,
which covers following triggers.
 - traceon-traceoff trigger
 - enable/disable_event trigger
 - snapshot trigger
 - stacktrace trigger
 - trigger filters

Here is the test result.

  ----
  # ./ftracetest test.d/trigger/
  === Ftrace unit tests ===
  [1] event trigger - test event enable/disable trigger   [PASS]
  [2] event trigger - test trigger filter [PASS]
  [3] event trigger - test snapshot-trigger       [PASS]
  [4] event trigger - test stacktrace-trigger     [PASS]
  [5] event trigger - test traceon/off trigger    [PASS]

  # of passed:  5
  # of failed:  0
  # of unresolved:  0
  # of untested:  0
  # of unsupported:  0
  # of xfailed:  0
  # of undefined(test bug):  0
  ----

Link: http://lkml.kernel.org/r/12b9c2b289a0dc1e4386e7b77674611a83abca85.1457029949.git.tom.zanussi@linux.intel.com
Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Shuah Khan <shuahkh@osg.samsung.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Tom Zanussi <tom.zanussi@linux.intel.com>
Reviewed-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>