Add rule about 'localhost'

plugins/mysql/mysql.go

@@ -77,6 +77,10 @@ var mappings = []*mapping{
 }
 
 func (m *Mysql) gatherServer(serv string, acc plugins.Accumulator) error {
+	if serv == "localhost" {
+		serv = ""
+	}
+
 	db, err := sql.Open("mysql", serv)
 	if err != nil {
 		return err

plugins/postgresql/postgresql.go

@@ -69,7 +69,7 @@ func (p *Postgresql) Gather(acc plugins.Accumulator) error {
 }
 
 func (p *Postgresql) gatherServer(serv *Server, acc plugins.Accumulator) error {
-	if serv.Address == "" {
+	if serv.Address == "" || serv.Address == "localhost" {
 		serv = localhost
 	}