tests: fix imports and test collection under some environments

While packaging json-logging for NixOS, I've come across two issues
with tests.  Since neither are specific to NixOS (though they may be
an artifact of how the build environment is set up), I felt it'd be
better to try to stream the fixes up.

- While testing, the import test for Quart finds not the 'quart'
  package, but tests/smoketests/quart.  It's been a while since I
  worked on this, but it seems to happen because pytest prepends
  the test module directory to sys.path by default [1].  To make
  it work with a default pytest invocation, we can simply try to
  import something only the real quart package provides.

- If no smoketest backends are specified, it will try to find tests
  in a __pycache__ directory [2] if it exists.

[1]: https://docs.pytest.org/en/stable/pythonpath.html
[2]: https://www.python.org/dev/peps/pep-3147/

Author: AluisioASG

json_logging/framework/quart/__init__.py

@@ -12,7 +12,7 @@
 def is_quart_present():
     # noinspection PyPep8,PyBroadException
     try:
-        import quart
+        from quart import Quart
         return True
     except:
         return False

tests/smoketests/test_run_smoketest.py

@@ -26,7 +26,7 @@ def collect_backends():
         yield preset_backend
     else:
         for folder in Path(__file__).parent.iterdir():
-            if folder.is_dir():
+            if folder.is_dir() and folder.name != '__pycache__':
                 yield str(folder.name)