thin: do not flush when quering for thin percent

Since we may easily get blocked when checking for percentage
of thin-pool - do not flush and just show current values.
This avoids holding VG locked when pool is overfilled.

WHATS_NEW

@@ -1,5 +1,6 @@
 Version 2.02.130 - 
 ===================================
+  Read thin-pool data and metadata percent without flush.
   Detect blocked thin-pool and avoid scanning their thin volumes.
   Check if dm device is usable before checking its size (2.02.116).
   Extend parsing of cache_check version in configure.

lib/activate/dev_manager.c

@@ -1045,6 +1045,11 @@ static int _percent_run(struct dev_manager *dm, const char *name,
 				wait ? DM_DEVICE_WAITEVENT : DM_DEVICE_STATUS, 0, 0, 0)))
 		return_0;
 
+	/* No freeze on overfilled thin-pool, read existing slightly outdated data */
+	if (lv && lv_is_thin_pool(lv) &&
+	    !dm_task_no_flush(dmt))
+		log_warn("Can't set no_flush flag."); /* Non fatal */
+
 	if (!dm_task_run(dmt))
 		goto_out;