selftests: ftrace: Hide ftracetest logs from git

Hide ftracetest result log directory from git.

Link: http://lkml.kernel.org/r/147928404640.22982.13173364949326289032.stgit@devboxSigned-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

tools/testing/selftests/ftrace/.gitignore

+logs