sdk: Fix DefaultSpan raising an exception in use_span (#577)

Fixes the error caused by span.status in use_span.

As status is not included in opentelemetry.trace.Span, span.status in use_span may cause an error.
For example, when use_span is called with DefaultSpan, it causes the error below.

'DefaultSpan' object has no attribute 'status'

Author: gky360

opentelemetry-sdk/src/opentelemetry/sdk/trace/__init__.py

@@ -605,7 +605,8 @@ def use_span(
 
         except Exception as error:  # pylint: disable=broad-except
             if (
-                span.status is None
+                isinstance(span, Span)
+                and span.status is None
                 and span._set_status_on_exception  # pylint:disable=protected-access  # noqa
             ):
                 span.set_status(

opentelemetry-sdk/tests/trace/test_trace.py

@@ -107,6 +107,16 @@ def run_general_code(shutdown_on_exit, explicit_shutdown):
         out = run_general_code(False, False)
         self.assertTrue(out.startswith(b"0"))
 
+    def test_use_span_exception(self):
+        class TestUseSpanException(Exception):
+            pass
+
+        default_span = trace_api.DefaultSpan(trace_api.INVALID_SPAN_CONTEXT)
+        tracer = new_tracer()
+        with self.assertRaises(TestUseSpanException):
+            with tracer.use_span(default_span):
+                raise TestUseSpanException()
+
 
 class TestTracerSampling(unittest.TestCase):
     def test_default_sampler(self):