Configure BGP with ip addresses from user input.

This patch causes BGP configuration for SP-VCPE template to be updated with user provided IP addresses.

To do so, logical interfaces in core router are sent to OpenNaaS from the GUI (within create method),
and afterwards, model used to configure BGP is updated with data of received core router logical interfaces.

With the values correctly updated in the model, configuring BGP from the model requires no change.

Fixes issue OPENNAAS-873 
Together with #512 fixes bug OPENNAAS-848

NOTE: This pull request conflicts with previous one (#513). Please, merge one first and notify me, so I can fix the other one.