* debian/patches/ubuntu_local_settings.py: Set flexible
  default for ALLOWED_HOSTS that should be changed for production
  deployments (LP: #1214982).
* Fix (LP: #1216019):
  - debian/openstack-dashboard.{postinst, postrm}: Add/remove horizon
    user.  Ensure /etc/openstack-dashbard ownership.
  - debian/openstack-dashboard.conf: Run WSGIDaemonProcess as user
    horizon, set WSGIProcessGroup to horizon.
  - debian/patches/ubuntu_local_settings.py: Generate and load secret
    key from /etc/openstack-dashboard/secret_key.