Fix races in AppInitMain and others with lock and atomic bools

Summary:
Also rename parameters in txdb header to match those used in the cpp
file.

Backport of core PR11107

Test Plan:

make check

Launch the app

Reviewers: #bitcoin_abc, deadalnix, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Subscribers: teamcity, schancel

Differential Revision: https://reviews.bitcoinabc.org/D2235