Ignore *.cfg and *.crt in the openstack inventory (#672)

This allows our users to keep the ansible.cfg file in the inventory as
well as putting e.g. LDAP certificates in.

Fixes #481

playbooks/provisioning/openstack/sample-inventory/ansible.cfg

@@ -6,7 +6,7 @@ forks = 50
 timeout = 30
 host_key_checking = false
 inventory = inventory
-inventory_ignore_extensions = secrets.py, .pyc
+inventory_ignore_extensions = secrets.py, .pyc, .cfg, .crt
 gathering = smart
 retry_files_enabled = false
 fact_caching = jsonfile