MXS-1545: handling of slave file EOF refactoring

MXS-1545: handling of slave file EOF refactoring.

Some slave/router state are now checked before any WARN/ERROR messages
about slave file EOF.

The missing “next_file” is always logged with warn.

server/modules/routing/binlogrouter/blr_file.c

@@ -1714,8 +1714,8 @@ blr_file_next_exists(ROUTER_INSTANCE *router,
             strncpy(next_file, result.file, BINLOG_FNAMELEN);
             next_file[BINLOG_FNAMELEN] = '\0';
 
-            MXS_INFO("The next Binlog file from GTID maps repo is [%s]",
-                     bigbuf);
+            MXS_DEBUG("The next Binlog file from GTID maps repo is [%s]",
+                      bigbuf);
 
             spinlock_acquire(&slave->catch_lock);