Use a unique chain-id with each test

[evan-forbes]

Currently, we are using a chain-id == "private" for each test. Up to this point, this has worked perfectly, but now that we are collecting data to an external database for many different networks and tests, using a unique chain-id would allow us to easily distinguish between test runs/networks in that data base.

This was recently also changed in the tendermint e2e test in #970

[Bidon15]

Ref: #34

[evan-forbes]

closing as this is redundant to #34