Fix a bug where running test_runner.py --usecli would fail when built without bitcoin-cli
Summary:
Introduced in D2696. The existence check for bitcoin-cli did not account for --usecli.
Depends on D5781
Test Plan:
cmake -GNinja -DBUILD_BITCOIN_CLI=OFF .. test_runner.py
This fails pre-patch and passes post-patch.
Reviewers: #bitcoin_abc, deadalnix
Reviewed By: #bitcoin_abc, deadalnix
Differential Revision: https://reviews.bitcoinabc.org/D5788