Setup SSH Keys for the nova users on compute hosts

This is required for live migrations and resizes to work
* Creates the nova .ssh directory
* Sets up SSH private and public Keys
* Adds public key to authorized_keys file
* Sets StrictHostChecking=no for the nova user

Fixes #5
Fixes #6
Merge pull request #7 from andymcc/nova_key_fix

Setup SSH Keys for the nova users on compute hosts