Refactoring get_primary_interface to use get_list_of_routes (#1377)
Refactoring get_primary_interface to use get_list_of_routes (#1377)

* refactoring get_primary_interface to use get_list_of_routes

* following jasonzio advice to determine default route and primary values

* converting candidates to list for python 3.4; primary_route should be the candidate with the lowest metric

* converting candidates to list during generation instead of multiple later conversion

* using get_metric instead of lambda to assign primary_route

* cleaning module from unused variables; expliciting primary_interface; we don't actually need primary_metric

Azure/WALinuxAgent,rjschwei/WALinuxAgent,rjschwei/WALinuxAgent,hglkrijger/WALinuxAgent,Azure/WALinuxAgent,hglkrijger/WALinuxAgent