kunit: tool: Recommend --raw_output=all if no KTAP found

kunit: tool: Recommend --raw_output=all if no KTAP found

If no KTAP header is found in the kernel output (e.g., because the kernel
crashed before the KUnit executor was run), it's very useful to re-run the
test with --raw_output=all, as that will show any error output (such as a
stacktrace, log message, BUG, etc). This is not particularly intuitive,
however, as --raw_output=all is not well known.

Add an extra log line to advertise --raw_output=all in this case, as it's
a terrible user experience to just get "Did any KUnit tests run?"

Signed-off-by: David Gow <david@davidgow.net>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>