Add Neutron support to backend and UI

Change-Id: a23e45679628765b0234f55e01996bf3e24710000

Neutron networking serialization tests

add metadata_proxy_shared_secret attr

tunnel_id_range and neutron handler fixes

[nailgun] Fix flake8 and fix neutron net_verify task

[nailgun] Add mesh role to Neutron GRE mode

network config save fix

check_networks task stub

neutron config fixed at openstack.json

do not show private for neutron_config GET req

fix data structure in config serializer

check_networks task added

Neutron UI (frontend part)