selftests/ftrace: Introduce exit_pass and exit_fail

As same as other results, introduce exit_pass and exit_fail
functions so that we can easily understand what will happen.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>