Refresh source interface before usurping routes and addresses

The configuration of the source interface might have change since the start of
the chef-client run. Specifically when running in HA mode, pacemaker might have
assigned addtional virtual IP Addressed to the interface. If we don't refresh here
those IPs get lost.
Merge pull request #198 from rhafer/refresh-before-usurp

Refresh source interface before usurping routes and addresses