TypeError in database view error handle

In error handling code inside
openstack_dashboard/dashboards/project/databases/views.py,
DetailView.get_data, on the logging line:
            LOG.error('Unable to retrieve flavor details'
                      ' for database instance: %s') % instance_id

That line will always produce the following error:
    openstack_dashboard.dashboards.project.databases.views in get_data
    TypeError: unsupported operand type(s) for %: 'NoneType' and 'unicode'

It's just a parenthesis issue.

Change-Id: Id3b551bf393a4a10ee18b570e91ac3e474692f8b
Closes-Bug: 1304623
Merge "TypeError in database view error handle"