Add a delay to SSH connection to fix the deploy_node race condition

This patch might look a little "hackish", but it has solved the terrible `deploy_node` race condition for me 100%. I've been using libcloud with this patch for a few days with a 100% success rate. It seems that the `timeout` argument for `_ssh_client_connect` is insufficient. In fact, it's set to 300 seconds by default, but the entire operation doesn't take nearly that long to fail, so that timeout must not be the proper thing to fix the `deploy_node` race condition. *This* fix, however, resolves the issue. 60 seconds is more than enough time to get the SSH key installed onto the node, even with the recent addition of `ssh_alternate_usernames`, which we suspect to be the culprit of this new race condition.

Please, let me know if there's anything I can do to improve upon this patch and get it merged in. This is really a critical bug that needs to be resolved quickly.
Edit - Is this getting thrown as an exception or just printed in the debug log?

If it's just printed in the paramiko's debug log, than it's normal and not actually an error. It simply means you are not using an DSA key (probably using RSA). If you are, in fact using DSA key, then it means that the key is corrupted and retrying won't change or fix anything.

Similar debug message is also printed when connecting with openssh-client in debug mode (`ssh -vvv`).