IPaddr2: add local scripts

Recently IPaddr got back handy hooks for local start and stop scripts. I find them handy and think that in certain situations such hooks can be useful in IPaddr2 too. Also that would make semantics of both script more coherent.

```
OCF_RESKEY_local_start_script
OCF_RESKEY_local_stop_script
```

My initial reason for getting such functionality is a result of using Cluster IP option in the IPaddr2. Enabling it brings ip_conntrack as a dependency which without additional iptables rules tries to track all the traffic routed through the host. On busy sites that very quickly overflows conntrack table and leads to the problems with the new and existing connections.

iptables allows to exclude certain traffic from tracking by using NOTRACK target in the raw table.

Having simple script that mangles iptables on start and stop of the RA makes the problem disappear.

I can imagine other situations when it is necessary to perform some additional actions on RA start and stop.

So, would it be possible to add local start/stop script hooks to IPaddr2 as well?

With regards,
Timur Bakeyev.

Start by comparing the IPaddr2 resource agent with IPaddr, focusing on how OCF_RESKEY_local_start_script and OCF_RESKEY_local_stop_script are handled. Trace the start and stop actions and verify that the requested hooks can support the described iptables NOTRACK setup while keeping both agents' semantics coherent.

Written by the indexing model from the issue text.