* Don't use /etc/openstack-dashboard for in-process generated data
  (LP: #1233752):
  - d/openstack-dashboard.{dirs,postinst}:
    + Create /var/lib/openstack-dashboard with restricted permissions,
      allowing www-data user to write a secret_key if need be.
    + Move /etc/openstack-dashboard/secret_key to correct location if
      it already exists.
  - d/p/ubuntu_settings.patch: Use /var/lib/openstack-dashboard for
    secret key storage instead of /etc/openstack-dashboard.