Move finalization suck as reconsiderblock actualy reconsider blocks

Summary:
Right now, if we reconsider a block that has been excluded due to finalization, this block will immediately get excluded again and not actually be reconsidered.

To ensure it is, move the finalization to the last common ancestor betweent he finalized block and the reconsidered block before reconsidering.

Test Plan: Added integration test.

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D2118