fix(E2E): ensure miniooni.bash is WAI (#972)

This diff re-enables `E2E/miniooni.bash`. To make it working properly, we
needed to figure out which were the right cloudfronts to use.

I looked into the configuration and determined that both cloudfronts
should be used because they basically map to the same host.

I also determined it was backwards to test a mixture of prod and testing
APIs, and probably also flaky. So, I  choose to only test the prod.

Additionally, I added support for testing all supported tunnels.

Closes https://github.com/ooni/probe/issues/2336

internal/engine/session.go

@@ -193,6 +193,8 @@ func NewSession(ctx context.Context, config SessionConfig) (*Session, error) {
 			config.Logger.Infof("tunnel '%s' running...", proxyURL.Scheme)
 			sess.tunnel = tunnel
 			proxyURL = tunnel.SOCKS5ProxyURL()
+		case "none":
+			proxyURL = nil // explicit way of saying we don't want to use a tunnel
 		}
 	}
 	sess.proxyURL = proxyURL