Add tests to check for eth_call side effects

[MicaiahReid]

If i'm not \wrong about the above then we don't yet have exhaustive tests that check if eth_call has side effects and we should add those.

Originally posted by @davidmurdoch in #2565 (comment)

[davidmurdoch]

We do have a test ("does not create a transaction on the chain" -- which is not a very robust test). The new code introduced in #2565 modifies state directly now, so we need to be extra careful that those state changes don't stick around.

[davidmurdoch]

I think we can consider this as implemented in #2565