Merge pull request #2667 from wpaulino/random-htlc-holder-sigs-non-anchors

Use sign_holder_htlc_transaction to sign non-anchors holder HTLCs

diff --cc lightning/src/chain/onchaintx.rs
Simple merge

diff --cc lightning/src/ln/channel.rs
Simple merge

diff --cc lightning/src/ln/monitor_tests.rs
Simple merge