Use ansible 2.12 for testcases_prepare (#8763)
Use ansible 2.12 for testcases_prepare (#8763)

tests/requirements.txt links to tests/requirements-2.12.txt, so
Kubespray uses ansible 2.12 by default for testing. However we
forgot to update testcases_prepare.sh to use ansible 2.12.
This updates testcases_prepare to use ansible 2.12.
kubernetes-sigs/kubespray,kubernetes-sigs/kubespray,kubernetes-sigs/kubespray,Atoms/kubespray,Atoms/kubespray,Atoms/kubespray,Atoms/kubespray,kubernetes-sigs/kubespray