[SRU] fix panko-daemons autopkgtest curl failure

[Impact]

panko-daemons autopkgtests is failing

Further inspection shows:

2019-10-17 13:38:56.754505 File "/usr/bin/panko-api", line 52, in <module>
2019-10-17 13:38:56.754517 application = build_wsgi_app()
2019-10-17 13:38:56.754530 File "/usr/lib/python3/dist-packages/panko/api/app.py", line 76, in build_wsgi_app
2019-10-17 13:38:56.754540 return load_app(service.prepare_service(argv=argv))
2019-10-17 13:38:56.754552 File "/usr/lib/python3/dist-packages/panko/api/app.py", line 64, in load_app
2019-10-17 13:38:56.754562 raise cfg.ConfigFilesNotFoundError([conf.api_paste_config])
2019-10-17 13:38:56.754585 oslo_config.cfg.ConfigFilesNotFoundError: Failed to find some config files: api_paste.ini

Appears to be a permissions issue with group not having access to /etc/panko.

[Test Case]
Run autopkgtests and curl command should be successful.

[Regression Potential]
Very low. The change involves modifications to the default apache2 site config for the panko API. It will be aligned with what the rest of the OpenStack packages use.