sdk-go has been updated twice recently, and testground is not up-to-date with it.

@hacdias please upgrade testground and test plans within testground to be conformant with testground/sdk-go#34

I am already upgrading testground and test plans within testground to be conformant with testground/sdk-go#31 at #1154 , so you can just lock testground to a commit such as testground/sdk-go@ab16330 (so that you don't have a lot of changes) and then I will move it forward.