Have rVPCs use the router.redundant.vrrp.interval setting

It defaults to 1, which is hardcoded in the template:
./cosmic/cosmic-core/systemvm/patches/debian/config/opt/cloud/templates/keepalived.conf.templ

As non-VPC redundant routers use this setting, I think it makes sense to use it for rVPCs as well.

We also need a change to pickup the cmd_line parameter and use it in the Python code that configures the router.

server/src/com/cloud/network/router/VirtualNetworkApplianceManagerImpl.java

@@ -1598,6 +1598,9 @@ Configurable, StateListener<VirtualMachine.State, VirtualMachine.Event, VirtualM
         if (isRedundant) {
             buf.append(" redundant_router=1");
 
+            final int advertInt = NumbersUtil.parseInt(_configDao.getValue(Config.RedundantRouterVrrpInterval.key()), 1);
+            buf.append(" advert_int=").append(advertInt);
+
             final Long vpcId = router.getVpcId();
             final List<DomainRouterVO> routers;
             if (vpcId != null) {