ntp_client: Wait for 4 sources which responded to request

To avoid '503 No such source error' in SLE when running chronyc sources while
chronyc is resolving sources and wait for response from 4 sources by default

https://bugzilla.suse.com/show_bug.cgi?id=1179022

tests/console/ntp_client.pm

@@ -24,6 +24,7 @@ sub run {
     if (is_sle) {
         systemctl 'enable chronyd';
         systemctl 'start chronyd';
+        assert_script_run 'until chronyc sources|grep "Number of sources = 4"; do sleep 1; echo "waiting for 4 ntp sources response"; done';
     }
 
     # ensure that ntpd is neither installed nor enabled nor active