Don't suppress OneDiff logging if client code has already defined handlers in parent logger

[rewbs]

With the current code, ConfigurableLogger.configure_logging() returns too soon if logging handlers are already defined in the parent logger.

If handlers are already defined, ConfigurableLogger should still set the OneDiff logging level and assign self.logger. The only step that should be skipped is setting up handlers (because the client code has already defined where logs should be sent).

[ccssu]

git pull git@github.com:rewbs/onediff.git rewbs/upstream-log-fix

👋 Hello @rewbs , thank you for your pr in OneDiff , PR is not a problem, please format it pip install -U black==19.10b0 click==8.0.0 && python -m black src/onediff/infer_compiler/utils/log_utils.py

[strint]

@rewbs Very happy to get your PR. Please help to fix the conflict and I will merge it.