[test runner] get native arch automatically
[test runner] get native arch automatically

use "uname -m" to get native arch

ostroproject/meta-iotqa,ostroproject/meta-iotqa,wanghongjuan/meta-iotqa-1,wanghongjuan/meta-iotqa-1,ostroproject/meta-iotqa,daweiwu/meta-iotqa-1,wanghongjuan/meta-iotqa-1,daweiwu/meta-iotqa-1,wanghongjuan/meta-iotqa-1,daweiwu/meta-iotqa-1,wanghongjuan/meta-iotqa-1,ostroproject/meta-iotqa,daweiwu/meta-iotqa-1,daweiwu/meta-iotqa-1,ostroproject/meta-iotqa