It looks like rhc app create nodebb nodejs-0.10 command did not create nodebb directory.
Please make sure, that you're running commands on your own computer, not through ssh on OpenShift side.
Try to remove nodebb from your OpenShift account and start from scratch.
Calling git init may seemed like it helped, but it created local only repository, which was not connected with any of the others (OpenShift, NodeBB and openshift-nodebb). That is why git push origin master did not work - origin remote was not configured.