Destroying images

Rigth now there is a bug when trying to destroy images.
Here is the problem
```
Chef::Log.debug("Destroying image: chef:#{container_name}")
image = Docker::Image.get("chef:#{container_name}")
image.delete
```
But in docker-api docs says that we should get the image by his ID
```
# Get Image from the server, with id
Docker::Image.get('df4f1bdecf40')
```

Reading the docs, this is hiding a 500 (meaning there is an issue with the Docker code).  Is there a corresponding bug filed in Docker itself?

I'd feel a lot more comfortable here if we did an if container.exists? (or its equivalent) rather than catching all 500's and saying they are OK.