dirmngr: Tune down err on missing ldapservers file

* dirmngr/dirmngr.c (parse_ldapservers_file): Tune down error
in case no such file exists.

--
This is hardly an error because by default such a file
does not exist. This caused trouble in support because
people think "Oh the system prints an error".

GnuPG-Bug-Id: T3539

dirmngr/dirmngr.c

@@ -1638,7 +1638,7 @@ parse_ldapserver_file (const char* filename)
   fp = es_fopen (filename, "r");
   if (!fp)
     {
-      log_error (_("error opening '%s': %s\n"), filename, strerror (errno));
+      log_info ("failed to open '%s': %s\n", filename, strerror (errno));
       return NULL;
     }