Make unit-tests output less verbose

It will capture output to stdout and stderr and print it when test is
failed. Please set LOGLEVEL env variable to INFO or DEBUG if you want
to see everything (as it was before).

setup.py

@@ -93,7 +93,12 @@ class PyTest(TestCommand):
             params['args'] += self.cov
         if self.junitxml:
             params['args'] += self.junitxml
-        params['args'] += ['--doctest-modules', MAIN_PACKAGE, '-s', '-vv']
+        params['args'] += ['--doctest-modules', MAIN_PACKAGE, '-vv']
+
+        import logging
+        silence = logging.WARNING
+        logging.basicConfig(format='%(asctime)s %(levelname)s: %(message)s', level=os.getenv('LOGLEVEL', silence))
+        params['args'] += ['-s' if logging.getLogger().getEffectiveLevel() < silence else '--capture=fd']
         errno = pytest.main(**params)
         sys.exit(errno)