CLOUDSTACK-1653: Redundant router: Fix check_heartbeat.sh malfunctional due to delayed cron job

The interval between keepalived.ts and keepalived.ts2 should be >= 60 seconds in
normal condition, because every 10 seconds keepalived.ts would be updated, and
at least every 60 seconds, keepalived.ts would be copy to keepalived.ts2.

If the interval is less than 60 seconds, then keepalived process failed to
update keepalived.ts every 10 seconds.

Take some delay of updating into consideration, check_heartbeat.sh would use 30
seconds as a way to tell keepalived process is alive or not.