add_client requires knowing provider
Here is an example of a command that will fail:
mallet add_client templates.LinodeClientVM norton.cfg clapping_dog
This fails because norton is not with Linode, ie. I picked the wrong provider. In an ideal world we would have automatically written the provder to norton.cfg when it was created, and we could then 'mallet add_client norton.cfg foobar' and be on our merry way. Failing that, we should be able to add the provider now and have mallet parse that.