selftests/ftrace: Add kprobe event with $comm argument testcase

Add kprobe-event with $comm argument testcase to
ftracetest. This not only checks syntax but
also checks log file.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Shuah Khan (Samsung OSG) <shuah@kernel.org>