Upgrade server dependencies, manage them with govendor

vendor/github.com/xenolf/lego/acme/utils.go

@@ -0,0 +1,29 @@
+package acme
+
+import (
+	"fmt"
+	"time"
+)
+
+// WaitFor polls the given function 'f', once every 'interval', up to 'timeout'.
+func WaitFor(timeout, interval time.Duration, f func() (bool, error)) error {
+	var lastErr string
+	timeup := time.After(timeout)
+	for {
+		select {
+		case <-timeup:
+			return fmt.Errorf("Time limit exceeded. Last error: %s", lastErr)
+		default:
+		}
+
+		stop, err := f()
+		if stop {
+			return nil
+		}
+		if err != nil {
+			lastErr = err.Error()
+		}
+
+		time.Sleep(interval)
+	}
+}