selftests/ftrace: Replace echo -e with printf

echo -e is not POSIX. Depending on what /bin/sh is, we can get
incorrect output like:
$ -e -n [1] Basic trace file check
$ -e 	[PASS]

Fix that by using printf instead.
Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Signed-off-by: Shuah Khan <shuah@kernel.org>

tools/testing/selftests/ftrace/ftracetest

@@ -173,8 +173,13 @@ strip_esc() {
 }
 
 prlog() { # messages
-  echo -e "$@"
-  [ "$LOG_FILE" ] && echo -e "$@" | strip_esc >> $LOG_FILE
+  newline="\n"
+  if [ "$1" = "-n" ] ; then
+    newline=
+    shift
+  fi
+  printf "$*$newline"
+  [ "$LOG_FILE" ] && printf "$*$newline" | strip_esc >> $LOG_FILE
 }
 catlog() { #file
   cat $1