Fixed "Scrape Duration" if psql down (prometheus-community#426)

Co-authored-by: Will Rouesnel <wrouesnel@wrouesnel.com>

Author: alexey-gavrilov-flant

cmd/postgres_exporter/postgres_exporter.go

@@ -1046,7 +1046,7 @@ func (s *Servers) GetServer(dsn string) (*Server, error) {
 var err error
 var ok bool
 errCount := 0 // start at zero because we increment before doing work
-retries := 3
+retries := 1
 var server *Server
 for {
 if errCount++; errCount > retries {