logging: fix early logging (#49)

Enable logging through logger objects early in the instantiation of
collectors. Without explicitly calling `logging.basicConfig()`, any
calls to `logging.getLogger(...).info(...)` and `...debug(...)` produce
no output until `logging.log(...)` or friends were called once.

p3exporter/__init__.py

@@ -29,6 +29,7 @@ def main():
     signal.signal(signal.SIGTERM, signal_handler)
     signal.signal(signal.SIGINT, signal_handler)
 
+    logging.basicConfig()
     logging.getLogger().setLevel(logging.INFO)
 
     parser = argparse.ArgumentParser(description="Python programmable Prometheus exporter.")