selftests/ftrace: Add a testcase for kprobe multiprobe event

Add a testcase for kprobe event with multi-probe.

Link: http://lkml.kernel.org/r/156095692637.28024.17188971794698768977.stgit@devnote2

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