If there is a SA flow error, display it in the test output

Something that keeps tripping me up with testing Smart Answers is the fact that the errors within the flow (incorrect response for question, that kind of thing) get swallowed up as part of the `current_state` object. Unless you explicitly do `puts current_state`, you wont see the error.

This adds a small `assert_not_error` which is automatically called as part of the other assertions.

This might not be the best way to do it (open to ideas) but it would be nice if we could come up with a way to have those errors properly displayed rather than having to manually throw `puts` statements around.