Move trove default test node to trusty.
Move trove default test node to trusty.

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

Change-Id: Id9fe9120fdd597c4d370d47ab9ad272db5fa2ccf

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