Add interface_for_ip function
Add interface_for_ip function

This patch adds a custom Puppet function called interface_for_ip
This function will be used within the TripleO puppet implementation
to help obtain the correct interface for a given IP address.

Change-Id: I0979f69a49052fda888277fa64ebeadc038bc778

paramite/puppet-tripleo,rdo-puppet-modules/puppet-tripleo,egafford/puppet-tripleo,rdo-puppet-modules/puppet-tripleo,openstack/puppet-tripleo,paramite/puppet-tripleo,paramite/puppet-tripleo,openstack/puppet-tripleo,rdo-puppet-modules/puppet-tripleo,openstack/puppet-tripleo,egafford/puppet-tripleo,egafford/puppet-tripleo