OpenStack operates on a private cloud model, so the instance types will be defined by the administrators of your own OpenStack service. The OpenStack instance types I have available to me aren't necessary the same as the ones you have - for what it's worth, I tested out cluster creation successfully with an m3.large instance on my local Cloudbreak server configured to connect to my OpenStack.
You'll need to work with the team that operates your OpenStack service to find out how to configure instances properly.
