Move AbortNode to shutdown and fix an error message

Summary:
Can be reviewed with the git option --color-moved=dimmed-zebra

Also fix a if (user_message.empty()) clause which was previously negated by mistake (introduced in D8649). This caused the specific user message to be overwritten by a more generic and less useful message.

This is a backport of core#21575 [3/6]
https://github.com/bitcoin/bitcoin/pull/21575/commits/fa91b2b2b3447a3645e7958c7dc4e1946a69cb9c

Depends on D11348

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D11349