Reset config before/after jaeger export tests

Some of its tests set env vars so they can be retrieved in the
Configuration; since some modules initialize it at load-time, it needs
to be reset before and after tests

exporter/opentelemetry-exporter-jaeger/tests/test_jaeger_exporter.py

@@ -41,6 +41,10 @@ def setUp(self):
         self._test_span = trace._Span("test_span", context=context)
         self._test_span.start()
         self._test_span.end()
+        Configuration._reset()
+
+    def tearDown(self):
+        Configuration._reset()
 
     def test_constructor_default(self):
         """Test the default values assigned by constructor."""
@@ -142,8 +146,6 @@ def test_constructor_by_environment_variables(self):
 
         environ_patcher.stop()
 
-        Configuration._reset()
-
     def test_nsec_to_usec_round(self):
         # pylint: disable=protected-access
         nsec_to_usec_round = jaeger_exporter._nsec_to_usec_round