Add more instance types

[joaquincasares]

https://github.com/joaquincasares/cassandralauncher/blob/master/cassandralauncher/cassandralauncher.py#L677

[rfarmaha]

Could these be updated as soon as possible?

[joaquincasares]

Hey @rfarmaha ,

Feel free to manually add or change any instance types you'd like for your local setup, or feel free to issue a pull request.

I won't be actively looking at keeping this list up to date since AWS instances are released frequently and randomly.

But the good thing is that it's easily accessible to hack. :)