Change other tests that generate cert chains to make use of the utility function.
Change other tests that generate cert chains to make use of the utility function.

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

docker/notary,HuKeping/notary,docker/notary,vdemeester/notary,docker/notary,endophage/notary,vdemeester/notary,jfrazelle/notary,endophage/notary,endophage/notary,johnsandiford/notary,vdemeester/notary,johnsandiford/notary,HuKeping/notary,jfrazelle/notary,HuKeping/notary,johnsandiford/notary,jfrazelle/notary