Make retry vars still hold in an authrization failer

[whockey]

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.

[brycebaril]

Thanks!