Demo application should have the configuration file

[Timur Nurlygayanov]

Steps To Reproduce:
1. Clone Mistral from the master branch amd run Mistral API service
2. Clone Mistral demo app from the commit: https://review.openstack.org/#/c/62361/
3. Run Mistral demo app:
cd mistral-demo-app
ln -s /home/xwizard/mistral/mistralclient mistralclient
tox
tox -evenv -- python demo_app/cmd/main.py

Observed Result:
we have no any configuration files for Mistral Demo app, but this app should pass the authentication in keystone to work with Mistral API service.
Error message with the following traceback:

Traceback (most recent call last):
  File "demo_app/cmd/main.py", line 34, in <module>
    from demo_app.api import client
  File "/home/ubuntu/mistral/mistral-demo-app/demo_app/api/client.py", line 22, in <module>
    project_name="mistral_demo")
  File "/home/ubuntu/mistral/mistral-demo-app/mistralclient/api/client.py", line 51, in __init__
    auth_url=auth_url)
  File "/home/ubuntu/mistral/mistral-demo-app/.tox/venv/local/lib/python2.7/site-packages/keystoneclient/v3/client.py", line 104, in __init__
    self.authenticate()
  File "/home/ubuntu/mistral/mistral-demo-app/.tox/venv/local/lib/python2.7/site-packages/keystoneclient/httpclient.py", line 468, in authenticate
    resp, body = self.get_raw_token_from_identity_service(**kwargs)
  File "/home/ubuntu/mistral/mistral-demo-app/.tox/venv/local/lib/python2.7/site-packages/keystoneclient/v3/client.py", line 165, in get_raw_token_from_identity_service
    '%s' % e)
keystoneclient.apiclient.exceptions.AuthorizationFailure: Authorization failed: Cannot authenticate without a valid auth_url