Move role specific vars to the role directory

This keeps vars that are specific to roles with the role, not
very well documented except in the playbook example here:
https://github.com/ansible/ansible/blob/devel/examples/playbooks/roletest.yml

This makes playbooks more concise since you do not have to explicitely
include vars for each roles, var_files will still override any of the
default values in <role>/vars/main.yml
adding comments
Merge pull request #10 from edx/feature/jarv/move-vars-to-role

Feature/jarv/move vars to role