[tests] Use FastRandomContext instead of boost::random::*

Summary:

Use FastRandomContext instead of
boost::random::{mt19937,uniform_int_distribution}.

Also include the fix from PR14093 fixing type mismatch (int truncated to
bool).

Backport of core PR10547 and PR14093
https://github.com/bitcoin/bitcoin/pull/10547/files
https://github.com/bitcoin/bitcoin/pull/14093/files

Test Plan:

./src/test/test_bitcoin -t scheduler_tests

Reviewers: #bitcoin_abc, deadalnix, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Differential Revision: https://reviews.bitcoinabc.org/D3275