Previous error message for invalid kunitconfig was vague. Added to it so
that it lists invalid fields and prompts for them to be removed.  Added
validate_config function returning whether or not this kconfig is valid.
Signed-off-by: NHeidi Fahim <heidifahim@google.com>
Reviewed-by: NBrendan Higgins <brendanhiggins@google.com>
Tested-by: NBrendan Higgins <brendanhiggins@google.com>
Signed-off-by: NShuah Khan <skhan@linuxfoundation.org>