Auto-finalize block once they reached a certain depth (by default 10)
This ensures that deep reorg are not possible.
Can be controlled by the -maxreorgdepth parameter. Set to -1 to disable.
Depends on D2083
Test Plan: Added an integration test.
Reviewers: #bitcoin_abc, jasonbcox
Reviewed By: #bitcoin_abc, jasonbcox
Subscribers: jasonbcox, teamcity
Differential Revision: https://reviews.bitcoinabc.org/D2102