Move src/test/bitcoin-util-test.py to test/util/bitcoin-util-test.py
Summary: This finishes the backporting of PR9956 from ore.
Test Plan:
make check ./test/functional/test_runner.py --extended
Reviewers: schancel, #bitcoin_abc, zquestz
Reviewed By: zquestz
Differential Revision: https://reviews.bitcoinabc.org/D956