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.
I see. It looks like it's an exception which we currently don't catch inside `_ssh_client_connect` method.

Currently we don't retry if this exception is throw which would explain the failure. A solution would be to modify `_ssh_client_connect` to also retry on this exception, although, I would really like to come to the root cause and figure out why this exception is being thrown in the first place.

Afaik, this exception has nothing to do with the connection and is thrown when parsing the key. This means that retrying shouldn't really fix it since key doesn't change during the life-time of `deploy_node` method and if this exception is throw it means the key is invalid and it doesn't make sense to retry. Unless, this is covering up a some other issue.