decouple from viper for filer store

weed/filer2/configuration.go

@@ -124,3 +124,13 @@ func (f *Filer) LoadConfiguration() {
 
 	os.Exit(-1)
 }
+
+// A simplified interface to decouple from Viper
+type Configuration interface {
+	GetString(key string) string
+	GetBool(key string) bool
+	GetInt(key string) int
+	GetInt64(key string) int64
+	GetFloat64(key string) float64
+	GetStringSlice(key string) []string
+}