ci: use the `v1.0` flavor of the docker images in the CI This new versioning will help us to maintain backward compatibility in the docker image. This will be useful to deal with mismatch between default/stable in version and the re-run CI on older changesets in the future. Once this changeset land on stable, we will have to merge it in default. Then we can start make backward incompatible changes in a new image version. Differential Revision: https://phab.mercurial-scm.org/D12388