schema[vars] validation matching limits role naming and is inconsistent with docs

[dansou901]

In the documentation, it says that the schema[vars] matches the patterns vars/*.yml and default/*.yml. In fact, due to 73b183b, it matches vars/**/*.yml as well. This means that in return I'm not able to name a role vars, because now the schema[vars] also matches vars/tasks/main.yml. Also, this pattern is not documented, which should be fixed. What do you think?