RFE: Add a "Test Template" button to the configuration UI

Right now, it's not easy for people to create a new template entry and get it working.

We should add some form of "test the template" button that verifies our ability to pull the image onto the docker cloud, possibly even going as far as starting a node.
That'll make it much easier for administrators to verify that they've fixed the issues - right now it's not easy for users to figure out why things aren't working.