Ignore __pycache__ directory when looking at roles

For some reason, locally "tox -e docs" on zuul-jobs creates a
roles/__pycache__ directory; I think because it has a __init__.py
because we need that to correctly find unit-tests
(I9a653666e8a083fb7f3fbb92589fe0467a41e6e6).  I can not seem to
convince it to not write this directory.

Ignore __pycache__ directories when matching.

Change-Id: If7e70456a31554317c419fcb2ad3aad1ad19c6bf

zuul_sphinx/zuul.py

@@ -188,6 +188,8 @@ class ZuulDirective(Directive):
             for p in os.listdir(d):
                 if not os.path.isdir(os.path.join(d, p)):
                     continue
+                if p in ('__pycache__',):
+                    continue
                 role_readme = os.path.join(d, p, 'README.rst')
                 if os.path.exists(role_readme):
                     roles[p] = role_readme