add gtest2 for testing
add gtest2 for testing

zuul layout[1] uses gtest2 project for testing so this project list should
include it.

[1]
http://git.openstack.org/cgit/openstack-infra/project-config/tree/dev/zuul/layout.yaml

Change-Id: Id3f93f3dcadf0480434e275057f284d71ae66c3e

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