Fix priority parameters for VIP instances

Prior this change, all Keepalived instances (except for OpenStack VIP)
had the same priority which leads to unpredictable master elections.

Change-Id: Ifdc468b83f904b36489830678e550fc82c206985
diff --git a/keepalived/cluster/instance/stacklight_monitor_vip.yml b/keepalived/cluster/instance/stacklight_monitor_vip.yml
index 28a6b69..05eb967 100644
--- a/keepalived/cluster/instance/stacklight_monitor_vip.yml
+++ b/keepalived/cluster/instance/stacklight_monitor_vip.yml
@@ -3,6 +3,8 @@
 classes:
 - service.keepalived.support
 parameters:
+  _param:
+    keepalived_stacklight_monitor_vip_priority: 101
   keepalived:
     cluster:
       enabled: true
@@ -12,4 +14,4 @@
           password: ${_param:keepalived_stacklight_monitor_vip_password}
           interface: ${_param:keepalived_stacklight_monitor_vip_interface}
           virtual_router_id: 100
-          priority: 101
+          priority: ${_param:keepalived_stacklight_monitor_vip_priority}