ftracetest: Add functions file that holds helper functions

ftracetest: Add functions file that holds helper functions

Created the file tools/testing/ftrace/test.d/functions that will
hold helper functions.

Current helper functions include:

 Add clear_trace() helper to reset the trace file

   Used as a descriptive name to show that "echo > trace" is clearing
   the trace file.

 Add disable/enable_tracing() helper calls

   Add calls that disable and enable tracing respectively by echoing
   0 or 1 into tracing_on.

 Add helper reset_tracer() function

    Add a helper function reset_tracer() that will clear the current_tracer
    (echo nop > current_tracer).

Link: http://lkml.kernel.org/r/20141103212737.696365174@goodmis.org
Link: http://lkml.kernel.org/r/20141104153028.465517119@goodmis.org
Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>