Send another UTXO if this is a neutrino backend. When sweeping anchors,
there are two transactions created, `local_sweep_tx` for sweeping
Alice's anchor on the local commitment, `remote_sweep_tx` for sweeping
her anchor on the remote commitment. Whenever the force close
transaction is published, Alice will always create these two
transactions to sweep her anchor.
On the other hand, when creating the sweep txes, the anchor itself is
not able to cover the fee, so another wallet UTXO is needed. In our
test case, there's a change output that can be used from the above
funding process. And it's used by both sweep txes - when `lnd` happens
to create the `remote_sweep_tx` first, it will receive an error since
its parent tx, the remote commitment, is not known, hence freeing the
change output to be used by `local_sweep_tx`. For neutrino client,
however, it will consider the transaction which sweeps the remote anchor
as an orphan tx, and it will neither send it to the mempool nor return
an error to free the change output. Thus, if the change output is
already used in `remote_sweep_tx`, we won't have UTXO to create
`local_sweep_tx`.
This commit adds the missing check for anchor sweep in test
`revoked_uncooperative_close_retribution_altruist_watchtower`, also
change the mempool check a bit so it's easier to track.
This commit clarifies the htlc failure case in the lncli payment
command, by using the cardinal number as well as 'hop' in the
failure message.
[skip ci]
This commit replaces the clock used in the unit test
`TestMailBoxAddExpiry`. Previously the `TestClock` is used, resulting in
the unit test being not so "unit" as the maintainer needs to know the
detailed implementation of `clock.Clock`, resulting in debugging a
failed unit test more difficult as the cognitive cost is high.
Re-implement `clock.Clock` also means we need to maintain more. This is
now solved by using mock clock so we can ignore the implementation
details and care only the returned results.
