Make retry vars still hold in an authrization failer

Only resetting the the retry_vars if the connection is actually established. Otherwise the reconnection could infinitely attempt to reconnect on an auth failure regardless of ```max_attempts```, ```retry_delay``` etc. 

__Example:__

1. Send in ```max_attempts:5```
2. Redis accepts the socket connection, but rejects at the auth level (invalid auth, max clients etc)
3. ```node_redis``` thought the connection was successful and reset the rety_vars 
4. However, ```do_auth``` emits an ```error``` event on a failure auth, which starts a reconnection


This change only resets the retry variables if the connection was actually successful.