test: add a --repeat argument to test_runner.py
Summary: This allows repeating the test suite or invidual tests a specified number of time, with the benefit of parallelism.
Test Plan:
ninja check-functional
$ test/functional/test_runner.py --repeat 50 p2p_leak rpc_dumpt* ... p2p_leak.py | ✓ Passed | 6 s p2p_leak.py | ✓ Passed | 6 s p2p_leak.py | ✓ Passed | 6 s p2p_leak.py | ✓ Passed | 6 s ... rpc_dumptxoutset.py | ✓ Passed | 0 s rpc_dumptxoutset.py | ✓ Passed | 1 s rpc_dumptxoutset.py | ✓ Passed | 1 s rpc_dumptxoutset.py | ✓ Passed | 1 s ALL | ✓ Passed | 333 s (accumulated) Runtime: 18 s
Reviewers: #bitcoin_abc, Fabien
Reviewed By: #bitcoin_abc, Fabien
Subscribers: Fabien
Differential Revision: https://reviews.bitcoinabc.org/D18054