selftests/ftrace: Add instance indication in test log

Add instance test indication in test log too.
Current ftracetest shows instance test indication on
the list of test, but not in the log for each test.

This adds instance test indication on the top of
each log, like below;

execute (instance) : /ftrace/test.d/ftrace/func_set_ftrace_file.tc

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>