Fix CHEF-3694 caused by bad resource naming

Two resources have the same name, which leads to:

Cloning resource attributes for database_user[create dashboard database user] from prior resource (CHEF-3694)
Previous database_user[create dashboard database user]: /var/chef/cache/cookbooks/nova_dashboard/recipes/server.rb:177:in `from_file'
Current  database_user[create dashboard database user]: /var/chef/cache/cookbooks/nova_dashboard/recipes/server.rb:187:in `from_file'
Merge pull request #79 from vuntz/fix-CHEF-3694

Fix CHEF-3694 caused by bad resource naming