cqlsh lost the ability to have a request wait indefinitely

In commit c7f0032912798b5e53b64d8391e3e3d7e4121165, when client_timeout became request_timeout, the logic was changed so that you can no longer use a timeout of None, despite the docs saying that you can:

https://docs.datastax.com/en/cql/3.3/cql/cql_reference/cqlshUsingCqlshrc.html#cqlshUsingCqlshrc__request-timeout