ftracetest: Use logfile name supported by busybox's mktemp

ftracetest: Use logfile name supported by busybox's mktemp

When I run the ftracetest in a busybox docker container, I saw
following error.  Make the logfile template to comply with busybox's
mktemp.  It also keep the logfiles under the logs directory.

  # /linux/tools/testing/selftests/ftrace/ftracetest
  === Ftrace unit tests ===
  mktemp: unrecognized option `--tmpdir=/linux/tools/testing/selftests/ftrace/logs/20141106-003624/'
  BusyBox v1.22.1 (2014-05-22 23:22:11 UTC) multi-call binary.

  Usage: mktemp [-dt] [-p DIR] [TEMPLATE]

  Create a temporary file with name based on TEMPLATE and print its name.
  TEMPLATE must end with XXXXXX (e.g. [/dir/]nameXXXXXX).
  Without TEMPLATE, -t tmp.XXXXXX is assumed.

  	-d	  Make directory, not file
  	-q	  Fail silently on errors
  	-t	  Prepend base directory name to TEMPLATE
  	-p DIR	  Use DIR as a base directory (implies -t)
  	-u Do not create anything; print a name

  Base directory is: -p DIR, else $TMPDIR, else /tmp

  [1] Basic trace file check/linux/tools/testing/selftests/ftrace/ftracetest: line 244: can't create : nonexistent directory
  /linux/tools/testing/selftests/ftrace/ftracetest: line 244: can't create : nonexistent directory
						  [FAIL]

Link: http://lkml.kernel.org/r/1415239470-28705-1-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>