Use URI when checking for repeated repos

[toliver]

When we check that the same repository hasn't been checked out in base_deps and base, we should check that based on the URI of the repo instead of the directory name (that can be freely assigned and is not unique).

This can be found here: https://github.com/shadow-robot/sr-build-tools/blob/master/ansible/roles/ros_workspace/tasks/main.yml#L93-L95