Can override each role's install path

Defaults to the system wide `roles-path` when `path` is not specified in the
provided `role-file`.  An example installing nginx to a relative path specified
by the `role-file`.

    - src: https://github.com/bennojoy/nginx
      path: vagrant/roles/
Merge pull request #8789 from retr0h/retr0h/add-role-path-to-role-file

Can override each role's install path