Make conntest output copy-pastable; fix go vet issues

devices/ssd1306/ssd1306smoketest/ssd1306smoketest.go

@@ -165,7 +165,7 @@ func (s *SmokeTest) run(i2cBus i2c.Bus, spiBus spi.ConnCloser, dc gpio.PinOut, w
 	}
 
 	s.devices = []*ssd1306.Dev{i2cDev, spiDev}
-	fmt.Printf("%s: Devices:   %s,   %s\n", s, s.devices[0], s.devices[1])
+	fmt.Printf("%s: Devices:   %v,   %v\n", s, s.devices[0], s.devices[1])
 	s.printStr("NewXXX() durations")
 
 	// Preparations.

devices/tm1637/tm1637_test.go

@@ -59,7 +59,7 @@ func TestNew(t *testing.T) {
 func TestDigits(t *testing.T) {
 	expected := []byte{0x3F, 0x06}
 	if b := Digits(0, 1); !bytes.Equal(b, expected) {
-		t.Fatal("%v != %v", b, expected)
+		t.Fatalf("%v != %v", b, expected)
 	}
 }