Use Nic.master instead of calling separate methods

Nic.master now also checks if an interface is enslaved into an ovs bridge.
Merge pull request #213 from rhafer/pull-req-release-pebbles-master-fe6235d7a36ecb5fb03d7dc3628236c4743f2296

Enhance Nic.master for ovs virtual switches [2/2]