This commit adds a test for a hold invoice which is accepted
off-chain, and held by the recipient until it expired and
the payer force-closes the channel. With this test we
demonstrate two bugs in our handling of hold invoice state
in the invoice registry when we expire on chain:
- Htlcs not updated: even when we've timed out, we don't
update the htlc state accordingly.
- Invoice can be settled: the invoice can be settled even
though it's expired on chain.
