Check writing trust bundle certificate to temporary file in binary format

```
 +++ b/openstack-heat-plugin-venafi/resources/venafi_certificate.py
@@ -247,7 +247,7 @@ class VenafiCertificate(resource.Resource):
     else:
       tmp_dir = tempfile.gettempdir()
 
-      f = open(path.join(tmp_dir, 'venafi-temp-trust-bundle.pem'), "w+")
+      f = open(path.join(tmp_dir, 'venafi-temp-trust-bundle.pem'), "wb+")
```