Cluster test: 02 unit more reliable waiting for slave sync.

tests/cluster/tests/02-failover.tcl

@@ -18,6 +18,14 @@ test "Instance #5 is a slave" {
     assert {[RI 5 role] eq {slave}}
 }
 
+test "Instance #5 synced with the master" {
+    wait_for_condition 1000 50 {
+        [RI 5 master_link_status] eq {up}
+    } else {
+        fail "Instance #5 master link status is not up"
+    }
+}
+
 set current_epoch [CI 1 cluster_current_epoch]
 
 test "Killing one master node" {