Update dockertest to only test 1.10, 1.11, and 1.12, and to be able to download the tgzs
Update dockertest to only test 1.10, 1.11, and 1.12, and to be able to download the tgzs

Signed-off-by: Ying Li <f39392f1e2d21dabc2bc5ab11d2bf832bde87b60@docker.com>

andrewhsu/notary,jfrazelle/notary,vdemeester/notary,andrewhsu/notary,endophage/notary,andrewhsu/notary,johnsandiford/notary,HuKeping/notary,vdemeester/notary,johnsandiford/notary,docker/notary,docker/notary,endophage/notary,umayr/notary,vdemeester/notary,dqminh/notary,HuKeping/notary,umayr/notary,endophage/notary,jfrazelle/notary,johnsandiford/notary,dqminh/notary,HuKeping/notary,dqminh/notary,docker/notary,umayr/notary,jfrazelle/notary