Move neutron default test node to trusty.
Move neutron default test node to trusty.

This change will run all neutron and neutron specs python27 unittests,
doc builds, and flake8 jobs on trusty nodes.

Change-Id: I263fe02ee91a2deebc0ecb258a5705d1015e9664

open-switch/infra_project-config,dongwenjuan/project-config,coolsvap/project-config,osrg/project-config,Tesora/tesora-project-config,openstack-infra/project-config,dongwenjuan/project-config,osrg/project-config,anbangr/osci-project-config,Tesora/tesora-project-config,anbangr/osci-project-config,openstack-infra/project-config,noorul/os-project-config,noorul/os-project-config,coolsvap/project-config,citrix-openstack/project-config,citrix-openstack/project-config,open-switch/infra_project-config