This modifies autoroles to raise a warning when it finds a role
without a README.rst file. This can be disabled with a config option
if you wish to build with warning-as-error but don't wish to document
roles.
Fix a typo in the readme for the zuul_role_paths
Add a test for the autoroles path detection by including a roles
directory under a subdir. Manually removing the README.rst file has
validated that the warning is triggered.
Change-Id: Ia64298e6e910d21eb6f3830dd8b42e40e3444fa8
a5136b73ad