[backport] Merge #15943: tests: Fail if RPC has been added without tests
fad0ce59e9 tests: Fail if RPC has been added without tests (MarcoFalke)
Need to be run with --coverage
Backport of Core PR15943
Test Plan:
test_runner.py --coverage --extended
Verify All RPC commands covered.
is printed to the console.
Differential Revision: https://reviews.bitcoinabc.org/D5743