When I create an app, this is the relevant snippet I get:
Cloning into 'tsunade23'...
The authenticity of host 'tsunade23-*.rhcloud.com (a.b.c.d)' can't be established.
RSA key fingerprint is *:*:::::*:*.
No matching host key fingerprint found in DNS.
Are you sure you want to continue connecting (yes/no)?
So, are you seeing the last 2 lines from my snippet when you create the app? If yes, just type 'yes' and you should be good to go.
Let me know if this isn't the case.