selftests/ftrace: Add syntax error test for multiprobe

Add syntax error test cases for multiprobe appending
errors.

Link: http://lkml.kernel.org/r/156095694541.28024.11918630805148623119.stgit@devnote2

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>