Parsing of redis url:s with database in it fails

[Grokzen]

If you pass in "redis://redis:6379/2" with a database parameter into the parse_url version in this lib it will fail out as the DB will be set implicitly and that will propegate automatically up to redis-py connection pool that will attempt to send SELECT command to redis when connection runs on_connect method and SELECT command is not supported when running a cluster node.

The proposed solution is to either strip out DB from the url before parsing it, or to hard fail when this is processed.