Wait for ssh to be ready before trying to connect.
Use openstack provided ssh key if key_name is specified in config.

Openstack allows users to upload public keys.  The user can then start
instances and use one of their uploaded keys to connect to the
instance.  Public keys are made available to the instances via the
metadata server and are placed on disk at boot.
Update README with new key_name option.
Merge pull request #2 from stevendanna/improve-ssh-setup

Allow users to use keys uploaded to Openstack