Reconnect timeout improvement

[DiegoRBaquero]

Minimum set at 15 seconds, each retry adds 30 seconds.

Fixes webtorrent#659

[alxhotel]

I think there should be a maximum, like 5 or 10 minutes

[DiegoRBaquero]

@alxhotel Agreed. Max of 5 minutes seems reasonable.

[feross]

The variance is important for when a tracker suddenly goes down and thousands of clients are trying to reconnect at the same time. If they all send requests in at the same time, it can be harder for the tracker to recover. I'd prefer to keep the variance in there.

Other improvements:

• The max should be raised to at least 20 minutes because if a tracker is down, checking every 5 minutes is much too frequently.
• The reconnect timeout should double each time, not merely increase linearly. So dead trackers reach the max time more quickly.

[feross]

FWIW, the default announce interval for an http/udp tracker is 30 minutes. So that might be a good vaue to set the maximum to.

[feross]

LGTM!

[feross]

7.5.2.