Update DevStack's local.conf sample

- Add sections on Swift and Trove
- Use CirrOS qcow2 image instead of UEC ones
Rename default qcow2 images during post-stack run

- Use `TestVM` for cirros qcow2 image
- Use `F20-x86_64-cfntools` for Fedora20 qcow2 image,
  as that is the name expected by default for AWS LoadBalancer
- Keep old names as description property of images
Use `TestVM` instead of cirros* as default image
Use `F20-x86_64-cfntools` name for fedora image
Use `demo` as default ssh key name
Update cloudconfig test template