Rename variables and move check for prefill.

See <agroal#226 (comment)>.
Do the check of the new primary in the very beginning.

Improves also the logs in debug mode to clearly indicate what is going
to happen to the old and new server.

Close agroal#224

src/libpgagroal/pool.c

@@ -802,14 +802,20 @@ void
 pgagroal_flush_server(signed char server)
 {
    struct configuration* config;
-   int newPrimary = (int)server;
+   int primary = -1;
+   bool prefill = false;
 
    pgagroal_start_logging();
    pgagroal_memory_init();
 
    config = (struct configuration*)shmem;
 
-   pgagroal_log_debug("pgagroal_flush_server %s", config->servers[server].name);
+   if (!pgagroal_get_primary(&primary))
+      prefill = server != (unsigned char)primary && primary != -1;
+   else
+      prefill = false;
+
+   pgagroal_log_debug("pgagroal_flush_server %s with%s prefill to %s", config->servers[server].name, prefill ? "" : "out", config->servers[primary].name);
    for (int i = 0; i < config->max_connections; i++)
    {
       if (config->connections[i].server == server)
@@ -850,10 +856,7 @@ pgagroal_flush_server(signed char server)
    {
       if (!fork())
       {
-         if (!pgagroal_get_primary(&newPrimary))
-            pgagroal_prefill(newPrimary != server);
-         else
-           pgagroal_prefill(false);
+         pgagroal_prefill(prefill);
       }
    }