SwapRecovery monitors payment of successful swap

[kilrau]

Successful LTC/BTC swap:

• swap took a while and execution was CTRL+C aborted on taker side
• swap still went through, showing in swaphistory on both sides
• swap payments show SUCCEEDED in lnd's on both sides

But xud log claims swap timeout: Maker: https://paste.ubuntu.com/p/xhKN53xKPG/

1. 17:49:11 received swapRequest, then typical swap messages back and forth
2. 17:49:21 sending payment
3. 17:49:48 SwapTimedOut

and maker swap recovery continues monitoring a successful outgoing payment:

10/06/2020 18:50:13.529 [SWAPS] debug: checking outgoing payment status for swap 6216f42a658d451e4756718fbffbf423ce93eaf2f0898a9d1c6bd207f77772e2
10/06/2020 18:50:13.533 [SWAPS] debug: swap for 6216f42a658d451e4756718fbffbf423ce93eaf2f0898a9d1c6bd207f77772e2 still has pending payments and will be monitored

TODO: @sangaman add your taker logs

[kilrau]

By @sangaman :

We've observed a failed swap on the maker side falling into SwapRecovery and remaining there even when the related outgoing LND payment appears to have been canceled and does not show up in the listpayments output for LND. Swaps that don't have pending outgoing payments should be removed from SwapRecovery and not continuously checked. This issue tracks this peculiarity.