support testnet configuration?

[michielbdejong]

This connector deployment configuration is hard-wired to XRP main net, see https://github.com/interledgerjs/tf-connector/blob/master/tier-1/salt/connector/files/launch.config.js#L19

Can we make that configurable, so that people can also use this repo to set up a connector on the testnet?

[sharafian]

We should definitely add testnet support, but I think I would set that up as a separate folder and separate section in the README.