Create SaltNova class

@techhat can you please take a look.

This was my idea behind everything, I included a check in there to make sure that novaclient was installed.  I put this just as an opt_requirement.txt.

This was how I see nova moving, and all of the cloud drivers moving to be more specialized in the future, so that we can include things through the drivers, but still only maintain one cloud state, so that it is portable between providers.

Thanks
Daniel