On master fw_fail_htlc is, especially on the CI, flaky.
We mine 100 blocks, then wait fixed 5 seconds, then check if bob has
failed back the htlcs to alice.
However if the test runs slowly (CI) 5 seconds can be too short
for bob to catch up to the new 100 mined blocks.
Instead we should just use the wait_until_htlcs_settled helper function
which polls Alice local_unsettled_sent with 30 sec timeout, allowing bob
to take a bit longer (or be faster) than 5 s.
```
.***** test_fw_fail_htlc ******
initializing alice
funding alice
a101c8c4c22043ff42029bcab2f0bf6ce5482a60d656294cbec3a4df557e2687
initializing bob
funding bob
d323d572c54817116d185c91f15e449550c651eb4ed76891d3011e0a8eb4ef9a
initializing carol
funding carol
bbf3503663876a4ae00f70c7e58ad49318e83d5cf99d6effe692e113d10910c2
mining 1 blocks
starting daemon (PID 5559)
/tmp/alice/regtest/wallets/default_wallet
true
starting daemon (PID 5577)
/tmp/bob/regtest/wallets/default_wallet
true
starting daemon (PID 5595)
/tmp/carol/regtest/wallets/default_wallet
true
alice and carol open channels with bob
mining 3 blocks
wait until alice sees channel open.
wait until alice sees channel open..
wait until alice sees channel open...
alice pays carol
Daemon stopped
mining 1 blocks
mining 150 blocks
wait until 99ad1d44b9054f5a85c2fb45e9a9b93eb13c785104ed0664be5cf866d79d38fc:2 is spent.
...
wait until 99ad1d44b9054f5a85c2fb45e9a9b93eb13c785104ed0664be5cf866d79d38fc:2 is spent............................
mining 1 blocks
mining 100 blocks
alice htlc was not failed
FDaemon stopped
```
f321x
36e9f185d2