Add support for multiple test cases in basic evm test suite

[s1na]

In #43 we merged a relayer that generates a scout config file based on a simplified version of add11 state test which doesn't use SSTORE and doesn't do metering. But it currently supports only that one test case. We should extend it to read multiple JSON files like add.json from the fixture dir and generate a scout yaml file for each of them.

We could alternatively generate one yaml file with multiple txes in its block, but we'll then only be able to check the postStateRoot after the whole block and not each individual tx. That's why I think generating multiple yaml files gives us more granular testing.