Enable automatic failover of l3 routers

When l3-agent is not working on a node, neutron server will
automatically move its routers to another l3-agent. Neutron server
detects l3-agent outage after 1-2 minutes, neutron-l3-agent is now
monitored every 30s by pacemaker which will restart the service in case of
a failure (this should cover most of outages). If outage is longer
(e.g. networking issue) and routers are reassigned to another node,
l3-agent will clean up routers from local node when it restarts (or when
it can communicate with neutron server again).

This solution is not perfect and doesn't cover some edge situations
described here: https://bugs.launchpad.net/neutron/+bug/1174591
But I think this still improves current state of l3-agent HA.

This should not be needed once neutron l3 agent HA patch is merged
(I83f2a5d2af42164c42773b385ba7b00872eed54e).

Change-Id: Ifd8d73b3b1a5b13095e87683449aa4cab7579d3e
Merge "Enable automatic failover of l3 routers"