Change RouteNexthopAttributes to RoutAttributes and remove the nh-attribute
from that structure. Also, change all the tests to now allocate NextHop objects
and pass those to inet6 routines in network_agent_mock. Also, change all API's
in network_agent_mock to accept NextHops object instead of strings.
Merge branch 'ipv6-devel2' of github.com:Juniper/contrail-dev-controller into ipv6-devel2