Rename playbook.yml to converge.yml

Migrates testing playbook name to the new name used in molecule v3.

Change-Id: I1dcad6039624e66f780a54dc8e65b8a221e65c00

doc/source/_exts/ansible-autodoc.py

@@ -296,7 +296,7 @@ class AnsibleAutoPluginDirective(Directive):
                 molecule_playbook_path = os.path.join(
                     molecule_path,
                     test,
-                    'playbook.yml'
+                    'converge.yml'
                 )
                 with open(molecule_playbook_path) as f:
                     molecule_playbook = DOCYAML.load(f.read())