Re-introduce Geth tests

[brianmcgee]

As part of #295 I had to remove the Geth tests. It appears the pre-generated datadir's being used are no longer compatible with latest Geth. We need to re-generate them and then re-introduce the tests.

[aldoborrero]

@brianmcgee what's the status of this one? If not relevant, let's close the issue.

[brianmcgee]

It's still relevant. In general we should be spinning up each client in a nixos test