Low: IPaddr2: improve add_interface function
Low: IPaddr2: improve add_interface function

* declare variables as local
* use ocf_run where appropriate
* use human-readable log messages

asp24/resource-agents,stevenraspudic/resource-agents,stevenraspudic/resource-agents,asp24/resource-agents,stevenraspudic/resource-agents,asp24/resource-agents