BOLT 3: add test vectors for htlc-transactions in case where CLTV is …

…used as tie-breaker for sorting (#539)

Add a serialized transactions test vector for the edge case of sorting htlc-timeout-tx
when there are multiple offered htlc with the same amount and preimage.

The test vector reuses previous preimages and creates a case scenario with 1 received htlc
and 2 offered, the two offered will have same scriptPubKey and redeemScript, but different CLTV value.

It is asserted the order in which the htlc transactions should be kept internally
and we assume the same order is used to construct the commitment_signed message.
This complements #491 .