fortio v1.17.1 - non ok http code logging consistency

Now both the fastclient (like before) and the std client will log http errors (#490)

Now both the fastclient (like before) and the std client will log non #490
ok http error codes (codes not 2xx or not 418) as they occur.
You can also turn off these warnings using -log-errors=false

Also log an id 0-n number of runners/connection for these messages (this is a log change
fast client logs look like

16:35:41 W http_client.go:806> [0] Non ok http code 503 (HTTP/1.1 503)

and std client:

16:35:25 W http_client.go:401> [0] Non ok http code 503

(#489)

Also use latest go 1.16 (1.16.9) in rev'ed up build image

Also updated the logos